Dissertations / Theses on the topic 'Ionic conductor'
To see the other types of publications on this topic, follow the link: Ionic conductor.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Ionic conductor.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Taksande, Kiran. "Exploration of the Ionic Conduction Properties of Porous MOF Materials." Thesis, Montpellier, 2022. https://ged.scdi-montpellier.fr/florabium/jsp/nnt.jsp?nnt=2022UMONS010.
Full textAbstract:
Ce travail a pour objectif l’étude de matériaux hybrides poreux de type Metal-Organic Frameworks (MOFs) et d’un cristal moléculaire en tant que conducteurs ioniques solides pour des applications dans le domaine de l’énergie et de l’environnement. Dans le premier cas, nous avons développé diverses stratégies pour optimiser et contrôler la teneur en sites acides de Lewis et en porteurs de charges de deux séries de MOFs afin de concevoir des matériaux aux propriétés de conduction protonique très prometteuses. A partir d’une approche basée sur la substitution progressive des ligands par des entités fonctionnalisées présentant des sources de protons acides, nous avons créé une série de MOFs, MIP-207-(SO3H-IPA)x-(BTC)1–x, dont la teneur en groupements sulfoniques, par l’intermédiaire du ligand SO3H-IPA, est contrôlée à façon. Le meilleur matériau qui combine stabilité structurale et conduction protonique élevée présente des performances sous humidité parmi les plus intéressantes au sein de la famille des MOFs conducteurs protoniques (e.g., σ = 2.6 × 10–2 S cm–1 à 363 K/95% d’humidité relative (RH)). Selon une autre approche, nous avons étudié un MOF mésoporeux connu (MIL-101(Cr)-SO3H) dont les parois des pores sont tapissées de sites protoniques et qui contient dans ses pores un liquide ionique, le chlorure chlorure de 1-Ethyl-3-methylimidazolium (EMIMCl) capable d’assurer le transfert de proton. L’encapsulation du liquide ionique, caractérisée par une série d’outils expérimentaux (sorption de diazote, DRX sur poudre, TGA/MS, DSC et analyse élémentaire), s’avère particulièrement efficace pour exalter les propriétés de conduction protonique des composites à la fois à l’état anhydre (σ473 K = 1.5 × 10-3 S cm-1) mais également à l’état hydraté (σ(343 K/60%-80%RH) ≥ 0.10 S cm-1). Enfin, ce travail a été étendu à une autre famille de solides poreux, à travers l’étude des propriétés de conduction ionique d’un cristal moléculaire à base de zirconium (Zr-3) qui contient des paires ioniques KCl. Nous avons démontré que ZF-3 transite d’un comportement isolant à l’état anhydre (σ = 5.1 x 10-10 S cm-1 à 363 K/0% RH) vers un comportement super-conducteur ionique en présence d’eau (σ = 5.2 x 10-2 S cm-1 à 363 K/95 % RH), suite à l’augmentation de la dynamique de ions Cl- sous hydratation. Par ailleurs, des simulations moléculaires ont permis de décrire les mécanismes microscopiques à l’origine des propriétés de conduction des matériaux étudiés. Ces avancées devraient permettre de développer dans le futur de nouveaux matériaux performants dans le domaine de la conduction protonique et ioniqueThe conductivity performance of a new series of chemically stable proton conducting Metal Organic Frameworks (MOFs) as well as a superionic molecular crystal was explored. The contribution of this PhD was to (i) select a variety of architectures and functionalities of robust MOFs/superionic molecular solids and (ii) characterize and rationalize their conducting performance over various temperature/humidity conditions. We designed two series of MOFs to achieve promising proton-conducting performance, using distinct approaches to modulate the concentration of Brønsted acidic sites and charge carriers and further boost the conductivity properties. First, a multicomponent ligand replacement strategy was successfully employed to elaborate a series of multivariate sulfonic-based solids MIP-207-(SO3H-IPA)x-(BTC)1–x which combine structural integrity with high proton conductivity values (e.g., σ = 2.6 × 10–2 S cm–1 at 363 K/95% Relative Humidity -RH-). Secondly, a proton conducting composite was prepared through the impregnation of an ionic liquid (1-Ethyl-3-methylimidazolium chloride, EMIMCl) in the mesoporous MIL-101(Cr)-SO3H. The resulting composite displaying high thermal and chemical stability, exhibits outstanding proton conductivity not only at the anhydrous state (σ473 K = 1.5 × 10-3 S cm-1) but also under humidity (σ(343 K/60%-80%RH) ≥ 0.10 S cm-1) conditions. Finally, the ionic conducting properties of another class of porous solids, considering a zirconium-formate molecular solid containing KCl ion pairs (ZF-3) were explored. ZF-3 switches from an insulator (σ = 5.1 x 10-10 S cm-1 at 363 K/0% RH) to a superionic conductor upon hydration (σ = 5.2 x 10-2 S cm-1 at 363 K/95 % RH), in relation with the boost of Cl- dynamics upon water adsorption. Noteworthy, quantum- and force-field based simulations were combined with the experimental approach to elucidate the microscopic mechanisms at the origin of the ionic conducting properties of the studied materials. This fundamental knowledge will serve to create novel robust superionic conductors with outstanding performances that will pave the way towards appealing societal applications for clean energy production
2
Taksande, Kiran. "Exploration of the Ionic Conduction Properties of Porous MOF Materials." Thesis, Université de Montpellier (2022-….), 2022. http://www.theses.fr/2022UMONS010.
Full textAbstract:
Ce travail a pour objectif l’étude de matériaux hybrides poreux de type Metal-Organic Frameworks (MOFs) et d’un cristal moléculaire en tant que conducteurs ioniques solides pour des applications dans le domaine de l’énergie et de l’environnement. Dans le premier cas, nous avons développé diverses stratégies pour optimiser et contrôler la teneur en sites acides de Lewis et en porteurs de charges de deux séries de MOFs afin de concevoir des matériaux aux propriétés de conduction protonique très prometteuses. A partir d’une approche basée sur la substitution progressive des ligands par des entités fonctionnalisées présentant des sources de protons acides, nous avons créé une série de MOFs, MIP-207-(SO3H-IPA)x-(BTC)1–x, dont la teneur en groupements sulfoniques, par l’intermédiaire du ligand SO3H-IPA, est contrôlée à façon. Le meilleur matériau qui combine stabilité structurale et conduction protonique élevée présente des performances sous humidité parmi les plus intéressantes au sein de la famille des MOFs conducteurs protoniques (e.g., σ = 2.6 × 10–2 S cm–1 à 363 K/95% d’humidité relative (RH)). Selon une autre approche, nous avons étudié un MOF mésoporeux connu (MIL-101(Cr)-SO3H) dont les parois des pores sont tapissées de sites protoniques et qui contient dans ses pores un liquide ionique, le chlorure chlorure de 1-Ethyl-3-methylimidazolium (EMIMCl) capable d’assurer le transfert de proton. L’encapsulation du liquide ionique, caractérisée par une série d’outils expérimentaux (sorption de diazote, DRX sur poudre, TGA/MS, DSC et analyse élémentaire), s’avère particulièrement efficace pour exalter les propriétés de conduction protonique des composites à la fois à l’état anhydre (σ473 K = 1.5 × 10-3 S cm-1) mais également à l’état hydraté (σ(343 K/60%-80%RH) ≥ 0.10 S cm-1). Enfin, ce travail a été étendu à une autre famille de solides poreux, à travers l’étude des propriétés de conduction ionique d’un cristal moléculaire à base de zirconium (Zr-3) qui contient des paires ioniques KCl. Nous avons démontré que ZF-3 transite d’un comportement isolant à l’état anhydre (σ = 5.1 x 10-10 S cm-1 à 363 K/0% RH) vers un comportement super-conducteur ionique en présence d’eau (σ = 5.2 x 10-2 S cm-1 à 363 K/95 % RH), suite à l’augmentation de la dynamique de ions Cl- sous hydratation. Par ailleurs, des simulations moléculaires ont permis de décrire les mécanismes microscopiques à l’origine des propriétés de conduction des matériaux étudiés. Ces avancées devraient permettre de développer dans le futur de nouveaux matériaux performants dans le domaine de la conduction protonique et ioniqueThe conductivity performance of a new series of chemically stable proton conducting Metal Organic Frameworks (MOFs) as well as a superionic molecular crystal was explored. The contribution of this PhD was to (i) select a variety of architectures and functionalities of robust MOFs/superionic molecular solids and (ii) characterize and rationalize their conducting performance over various temperature/humidity conditions. We designed two series of MOFs to achieve promising proton-conducting performance, using distinct approaches to modulate the concentration of Brønsted acidic sites and charge carriers and further boost the conductivity properties. First, a multicomponent ligand replacement strategy was successfully employed to elaborate a series of multivariate sulfonic-based solids MIP-207-(SO3H-IPA)x-(BTC)1–x which combine structural integrity with high proton conductivity values (e.g., σ = 2.6 × 10–2 S cm–1 at 363 K/95% Relative Humidity -RH-). Secondly, a proton conducting composite was prepared through the impregnation of an ionic liquid (1-Ethyl-3-methylimidazolium chloride, EMIMCl) in the mesoporous MIL-101(Cr)-SO3H. The resulting composite displaying high thermal and chemical stability, exhibits outstanding proton conductivity not only at the anhydrous state (σ473 K = 1.5 × 10-3 S cm-1) but also under humidity (σ(343 K/60%-80%RH) ≥ 0.10 S cm-1) conditions. Finally, the ionic conducting properties of another class of porous solids, considering a zirconium-formate molecular solid containing KCl ion pairs (ZF-3) were explored. ZF-3 switches from an insulator (σ = 5.1 x 10-10 S cm-1 at 363 K/0% RH) to a superionic conductor upon hydration (σ = 5.2 x 10-2 S cm-1 at 363 K/95 % RH), in relation with the boost of Cl- dynamics upon water adsorption. Noteworthy, quantum- and force-field based simulations were combined with the experimental approach to elucidate the microscopic mechanisms at the origin of the ionic conducting properties of the studied materials. This fundamental knowledge will serve to create novel robust superionic conductors with outstanding performances that will pave the way towards appealing societal applications for clean energy production
3
Osment, P. A. "Multipole NMR studies : Dynamics of some spin-3/2 systems." Thesis, University of York, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379029.
Full text
4
Zhang, Gong. "Modeling and characterization of mixed ionic-electronic conductor membranes for hydrogen separation." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/19018.
Full text
5
Akle, Barbar Jawad. "Characterization and Modeling of the Ionomer-Conductor Interface in Ionic Polymer Transducers." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/28682.
Full textAbstract:
Ionomeric polymer transducers consist of an ion-exchange membrane plated with conductive metal layers on its outer surfaces. Such materials are known to exhibit electromechanical coupling under the application of electric fields and imposed deformation (Oguro et al., 1992; Shahinpoor et al., 1998). Compared to other types of electromechanical transducers, such as piezoelectric materials, ionomeric transducers have the advantage of high-strain output (> 9% is possible), low-voltage operation (typically less than 5 V), and high sensitivity in the charge-sensing mode.
A series of experiments on actuators with various ionic polymers such as Nafion and novel poly(Arylene ether disulphonate) systems (BPS and PATS) and electrode composition demonstrated the existence of a linear correlation between the strain response and the capacitance of the material. This correlation was shown to be independent of the polymer composition and the plating parameters. Due to the fact that the low-frequency capacitance of an ionomer is strongly related to charge accumulation at the electrodes, this correlation suggests a strong relationship between the surface charge accumulation and the mechanical deformation in ionomeric actuators. The strain response of water-hydrated transducers varies from 50 μstrain/V to 750 μstrain/V at 1Hz while the strain-to-charge response is between 9 μstraincm2 and 15 μstraincm2. This contribution suggests a strong correlation between cationic motion and the strain in the polymer at the ionomer-conductor interface.
A novel fabrication technique for ionic polymer transducers was developed for this dissertation for the purpose of quantifying the relationship between electrode composition and transducer performance. It consists of mixing an ionic polymer dispersion (or solution) with a fine conducting powder and attaching it to the membrane as an electrode. The Direct Assembly Process (DAP) allows the use of any type of ionomer, diluent, conducting powder, and counter ion in the transducer, and permits the exploration of any novel polymeric design. Several conducting powders have been incorporated in the electrode including single-walled carbon nanotubes (SWNT), polyaniline (PANI) powders, high surface area RuO2, and carbon black electrodes. The DAP provided the tool which enabled us to study the effect of electrode architecture on performance of ionic polymer transducers. The DAP allows the variation in the electrode architecture which enabled us to fabricate dry transducers with 50x better performance compared to transducers made using the state of the art impregnation-reduction technique. DAP fabricated transducers achieved a strain of 9.4% at a strain rate of 1%/s. Each electrode material had an optimal concentration in the electrode. For RuO2, the optimal loading was approximately 45% by volume. This study also demonstrated that carbon nanotubes electrodes have an optimal performance at loadings around 30 vol%, while PANI electrodes are optimized at 95 vol%.
Extensional actuation in ionic polymer transducers was first reported and characterized in this dissertation. An electromechanical coupling model presented by Leo et al. (2005) defined the strain in the active areas as a function of the charge. This model assumed a linear and a quadratic term that produces a nonlinear response for a sine wave actuation input. The quadratic term in the strain generates a zero net bending moment for ionic polymer transducers with symmetric electrodes, while the linear term is canceled in extensional actuation for symmetric electrodes. Experimental results demonstrated strains on the order of 110 μstrain in the thickness direction compared to 1700 μstrain peak to peak on the external fibers for the same transducer, could be achieved when it is allowed to bend under +/-2V potential at 0.5 Hz. Extensional and bending actuation in ionic polymer transducers were explained using a bimorph active area model. Several experiments were performed to compare the bending actuation with the extensional actuation capability. The active area in the model was assumed to be the high surface area electrode. Electric double layer theory states that ions accumulate in a thin boundary layer close to the metal-polymer interface. Since the metal powders are evenly dispersed in the electrode area of the transducer, this area is expected to actuate evenly upon voltage application. This active area model emphasizes the importance the boundary layer on the conductor-ionomer interfacial area.
Computing model parameters based on experimental results demonstrated that the active areas model collapses the bending data from a maximum variation of 200% for the strain per charge, to less than 68% for the model linear term. Furthermore, the model successfully predicted bending response from parameters computed using thickness experimental results. The prediction was particularly precise in estimating the trends of non-linearity as a function of the amount of asymmetry between the two electrodes.Ph. D.
6
Liu, Jingjing. "Mass transport and electrochemical properties of La2Mo2O9 as a fast ionic conductor." Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/5566.
Full textAbstract:
La2Mo2O9, as a new fast ionic conductor, has been investigated widely due to its high ionic conductivity which is comparable to those of the commercialized materials. However, little work has been reported on the oxygen transport and diffusion in this candidate electrolyte material. The main purpose of this project was to investigate oxide ion diffusion in La2Mo2O9 and also the factors which could affect oxygen transport properties. Oxygen isotope exchange followed by Secondary Ion Mass Spectrometry (SIMS) measurements were employed to obtain oxygen diffusion profiles. A correlation between oxygen ion transport and the electrochemical properties such as ionic conductivity was built upon the Nernst Einstein equation relating the diffusivity to electrical conductivity. In-situ neutron diffraction and AC impedance measurements were designed and conducted to investigate the correlation between crystal structure and oxygen transport in the bulk materials. Other techniques, such as synthesis, microstructure studies, and thermal analysis were also adopted to study the electrochemical properties of La2Mo2O9. The results of the study on the effects of microstructure on oxygen diffusion in La2Mo2O9 revealed that the grain boundary component played a significant role in electrochemical performance, although the grain size seemed to have little influence on oxygen transport. The oxygen isotope exchange in 18O2 was successfully carried out by introducing a silver coating on the sample surface, which solved the main difficulty in applying oxygen isotope exchange on pure ionic conductors. The ionic conductivity obtained from the diffusion coefficients was consistent with the result from AC impedance spectroscopy. The number of mobile oxygen ions was estimated to be 5 per unit cell. There was a difference of oxygen self diffusion coefficient when the isotope exchange was conducted in 18O2 and H2 18O. The activation energy of oxygen diffusion in humidified atmosphere was higher than that measured in dry atmosphere. It indicated that the humidified atmosphere had affected oxygen transport in the material. The studies on hydroxyl incorporation and transport explained the decreased oxygen diffusion coefficients in wet atmosphere and also suggested proton conductivity in La2Mo2O9, which leads to further investigation on applications of La2Mo2O9 as a proton conductor. In-situ neutron diffraction and AC impedance measurement revealed a close relationship between crystal structure and ionic conductivity. The successful application of this technique provides a new method to simultaneously investigate crystal structure and electrical properties in electro-ceramics in the future.
7
Chiabrera, Francesco Maria. "Interface Engineering in Mixed Ionic Electronic Conductor Thin Films for Solid State Devices." Doctoral thesis, Universitat de Barcelona, 2019. http://hdl.handle.net/10803/667601.
Full textAbstract:
Interface-dominated materials such as nanocrystalline thin films have emerged as an enthralling class of materials able to engineer functional properties of transition metal oxides widely used in energy and information technologies. In this direction, it has been recently proved that grain boundaries (GBs) in the perovskite La1-xSrxMnO3±δ (manganite) deeply impact its functional properties, boosting the oxygen mass transport while abating the electronic and magnetic order. The impact of grain boundary in nanocrystalline thin films is so relevant to radically change the behaviour of the material, transforming an electronic conductor into a mixed ionic-electronic conductor functional for redox-based solid state devices. Based on these preliminary studies, it became crucial to understand the origin of this enhancement, in order to gain engineering capabilities and potentially extend it to other functional perovskite materials.
Following this approach, this thesis focuses in analysing the remarkable properties of GBs in manganites and, ultimately, investigating the possibility of engineering these interfaces. First, the structural and chemical characterization of the LSM thin films deposited by pulsed laser deposition (PLD) is presented. The compositional analysis of the layers revealed a severe Mn deficiency, ascribed to the plasma-background interactions during the deposition. The analysis of the GBs of these Mn-deficient thin films revealed a remarkable local modification of ionic composition, consisting in a Mn and O depletion along with a La and Sr enrichment (viz. GBdef). Then, through a PLD combinatorial approach, Mn was progressively inserted in the perovskite structure, altering the overall cationic ratio of the thin films (Mn/(La+Sr)). The variation of cationic chemical potential of the thin films was observed to significantly affect the GB composition, which passed from Mn depletion (La-enrichment) to Mn enrichment (La-depletion), while maintaining an O deficiency character (viz. GBrich). This behaviour suggests that through the tuning of the overall cationic concentration in the thin films the GB composition can be altered, offering an innovative way for engineering chemical defects in strained interfaces.
The effect of these different GBs on the electrical conductivity and the oxygen mass transport properties of LSM thin films with different Mn content was then measured. It was found that in the layers characterized by GBdef, the lack of Mn hinders the low temperature metal insulator transition and, in its place, a variable range hopping mechanism occurs, where electrons tunnels across the GBs for reaching distant Mn atoms. Moreover, a simultaneous decrease of activation energies of both GB oxygen diffusivity and GB oxygen surface exchange coefficient was observed further decreasing the Mn concentration in these thin films, indicating a strong interdependence between the two phenomena. The results suggest that the GB accumulation of oxygen vacancies is at the origin of the large improvement of both oxygen mass transport parameters observed in LSM polycrystalline thin films.
In LSM thin films characterized by GBrich, the low temperature metallic behaviour is progressively restored and an increase of electronic conductivity is observed in the entire temperature range. Additionally, in these layers relative changes of Mn do not give rise to a variation of the oxygen diffusivity, meaning that the GBs oxygen vacancy concentration is not altered anymore. Overall, the results demonstrate the possibility of engineering the functional properties of LSM polycrystalline thin films by modifying the GB cationic composition.
In the third part of the thesis, the effect of Co substitution on LSMC functional properties was investigated. The LSMC thin films were produced by combinatorial PLD, which allow a direct measure of real-continuous spread LSMC system. The oxygen mass transport properties of bulk and GB were evaluated by finite element model fitting of 18O exchange profiles. The results revealed that GBs enhance the transport properties of the whole material in the range of composition under study, although for high Co concentration the GB effect is concealed by the high bulk diffusion.
8
Toghan, Ahmed Arafat Ahmed [Verfasser]. "Electrochemical promotion of catalytic ethylene oxidation on a solid ionic conductor / Arafat Ahmed Toghan Ahmed." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2012. http://d-nb.info/103149815X/34.
Full text
9
Akin, Figen Tulin. "Ionic Conducting Ceramic Membrane Reactor for Partial Oxidation of Light Hydrocarbons." University of Cincinnati / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1021991903.
Full text
10
Tomita, Atsuko, Mitsuru Sano, Takashi Hibino, Yousuke Namekata, and Masahiro Nagao. "Intermediate-Temperature NOx Sensor Based on an In^3+ -Doped SnP2O7 Proton Conductor." The Electrochemical Society, 2006. http://hdl.handle.net/2237/18457.
Full text
11
Kidd, Bryce Edwin. "Cation and Anion Transport in a Dicationic Imidazolium-Based Plastic Crystal Ion Conductor." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/23300.
Full textAbstract:
Here we investigate the organic ionic plastic crystal (OIPC) 1,2-bis[N-(N\'-hexylimidazolium-d2(4,5))]C2H4 2PF6- in one of its solid plastic crystal phases by means of multi-nuclear solid-state (SS) NMR and pulsed-field-gradient (PFG) NMR. We quantify distinct cation and anion diffusion coefficients as well as the diffusion activation energies (Ea) in this dicationic imidazolium-based OIPC. Our studies suggest a change in transport mechanism for the cation upon varying thermal and magnetic treatment (9.4 T), evidenced by changes in cation and anion Ea. Moreover, variable temperature 2H SSNMR lineshapes further support a change in local molecular environment upon slow cooling in B0. Additionally, we quantify the percentage of mobile anions as a function of temperature from variable temperature 19F SSNMR, where two distinct spectral features are present. We also comment on the pre-exponential factor (D0), giving insight into the number of degrees of freedom for both cation and anion as a function of thermal treatment. In conjunction with previously reported conductivity values for this class of OIPCs and the Stokes-Einstein relation, we propose that ion conduction is dominated by anion diffusion between crystallites (i.e., grain boundaries). Using our experimentally determine diffusion coefficient and previously reported PF6- hydrodynamic radius (rH), viscous (" = 4.1 Pa " s) ionic liquid (IL) is present with a cation rH of 0.34 nm. NMR measurements are very powerful in elucidating fundamental OIPC properties and allow a deeper understanding of ion transport within such materials.Master of Science
12
Yamamoto, Takayuki. "Control of The Phase Transition Behavior and Ionic Conductivity of Silver Iodide Nanoparticles by Size, Pressure and Anion Mixing." Kyoto University, 2017. http://hdl.handle.net/2433/225993.
Full text
13
Kompany, Talieh. "Synthèse, caractérisation et propriétés catalytiques de phosphates de structure NASICON à base de cuivre, palladium et argent : application à l'oxydation ménagée des oléfines." Compiègne, 1990. http://www.theses.fr/1990COMPD235.
Full textAbstract:
La nouvelle phase Pd0,5 Zr2 (P O4)3 a été préparée. L'analyse des propriétés cristallographiques, structurale ont montré que cette phase cristallise dans une maille monoclinique et elle est isostructurale de CU0,5 Zr2 (PO4)3. L'élaboration, caractérisation des solutions solides (CUx Pdf-x)0,5 Zr2 (PO4)3 a montré que des substitutions Pd par CU est possible. L'étude, la comparaison des performances catalytiques des NASICON contenant CU1, CUII, CU-Pd, Ag ont montré que : les NASICON contenant ion de transition sont bien des catalyseurs d'oxydation ménagée du propylène. La réaction fait par un mécanisme redox. Les composés bicationiques sont plus performants. La réaction se fait par la participation des couples CUII / CUI, PdII / PdI. Dans le cas des composés monocationiques la réaction se fait par la formation des micro-domaines ion métalliques l'oxyde de l'ion à la surface du catalyseur.
14
Maas, Klaasjan. "La2NiO4+d, un conducteur mixte ionique-électronique pour les mémoires à changement de Valence." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAI012/document.
Full textAbstract:
Cette thèse porte sur la compréhension et le développement de matériaux innovants en tant que composant actif pour les mémoires résistives à changement de valence (VCM), qui constitue une sous-catégorie des mémoires résistives où des réactions d’oxydoréduction sont à l’origine du mécanisme de commutation résistive. Leur incorporation dans les circuits intégrés nécessite une tension (ou un courant) électrique pour lire et programmer la mémoire, cependant leurs fonctionnalités dépend essentiellement des propriétés chimiques des matériaux constituant la mémoire. Dans ce manuscrit nous étudions les propriétés du composé La2NiO4+δ, un conducteur mixte d’ions et d’électrons qui de par sa conduction d’ions oxydes dans le volume du matériau offre un terrain de jeu prometteur pour les VCMs. Nous avons pu obtenir des films minces de La2NiO4+δ fortement texturés sur des substrats monocristallins de SrTiO3 par dépôt chimique en phase vapeur à partir de l’injection pulsée de précurseurs métalorganiques (PiMOCVD). Des recuits sous atmosphère contrôlée ont permis de faire varier le contenu en oxygène et d’ajuster les propriétés semiconductrices-type p de La2NiO4+δ par un mécanisme d’auto-dopage. Une sur-stœchiométrie en oxygène dans la plage 0 ≤ δ ≤ 0.08 induit une variation de résistivité de 5.7 Ω.cm à 5.3x10-3 Ω.cm pour un recuit sous hydrogène ou sous oxygène, respectivement. Les films minces de La2NiO4+δ ont ensuite été utilisés comme base dans la conception d’hétérostructures métal/La2NiO4+δ/métal. Le rôle important de la jonction métal/oxyde sur les propriétés des VCMs de type interfaciales est discuté en détails. En particulier, un contact ohmique avec La2NiO4+δ est obtenu en utilisant un matériau d’électrode tel que le Pt ayant un travail de sortie élevé, alors qu’un contact rectifiant est obtenu avec Ti résultant de la présence d’une fine couche (~8 nm) de TiOx formée de manière spontanée à l’interface Ti/La2NiO4+δ. Une hétérojunction asymétrique Pt/La2NiO4+δ/Ti a été sélectionnée comme prototype afin d’évaluer les propriétés memristives de composants basés sur La2NiO4+δ. Un changement de résistance bipolaire a été mesuré ainsi qu’une possibilité de programmation largement multi-niveaux lorsque la mémoire est stimulée de manière pulsée. Les résultats prometteurs obtenus par ce premier prototype sont ensuite étendus pour la première fois à un système plus complexe de bicouches La2NiO4+δ/LaNiO3. Des propriétés de relaxation ont été mesurées, rendant ces mémoires intéressantes pour leur utilisation en tant que mémoire volatile pour un filtrage dynamique dans des applications neuromorphiquesThis thesis is focused on the understanding and development of novel materials for valence-change memories (VCMs), a type of resistive switching memories in which the memory storage mechanism is based on internal redox reactions. VCMs are in essence electrochemical systems. Their implementation in integrated electronic circuits relies on a voltage (or current) to measure and operate the memory, but their functionality is highly dependent on the chemical properties of the materials constituting the memory. In this work we present how the mixed ionic-electronic conducting La2NiO4+δ compound offers an interesting playground for VCM applications due to its intrinsic bulk oxygen-ion conducting properties. We have successfully prepared La2NiO4+δ in the form of highly oriented thin films on SrTiO3 single crystal substrates using pulsed-injection chemical vapour deposition (PiMOCVD). Post-annealing treatments in oxidizing/reducing atmospheres allow tuning the oxygen content and the p-type semiconducting properties of La2NiO4+δ due to a self-doping mechanism. The obtained oxygen over-stoichiometry in the 0 ≤ δ ≤ 0.08 range induced a variation of the film resistivity between 5.7 Ω.cm and 5.3x10-3 Ω.cm for hydrogen or oxygen-annealed samples, respectively. The optimized La2NiO4+δ thin films have been used as a base for the microfabrication of metal/La2NiO4+δ/metal heterostructures. The important role of the metal/oxide junction in interface-type VCMs is discussed in detail. In particular, an ohmic contact is obtained with La2NiO4+δ when using a high work function metal such as Pt, while rectifying contact properties are obtained when using Ti due to the presence of a spontaneously-formed TiOx interlayer (~8 nm) at the Ti/L2NO4 interface. An asymmetric Pt/La2NiO4+δ/Ti heterojunction has been selected as a first prototype to assess the memory capabilities of a La2NiO4+δ-based memristive device. A continuous bipolar analogue-type memory behaviour has been measured, together with strong multilevel programing capabilities when operated in pulsed mode. In addition, the promising results offered by this prototypical device have been extended for the first time to La2NiO4+δ/LaNiO3 bilayers, showing memory relaxation properties, which are potentially interesting for short-term memory and filtering applications in neuromorphic-based computational hardware
15
Lee, Chong-Hoon. "Study of reversible electrode reaction and mixed ionic and electronic conduction of lithium phosphate electrolyte for an electrolchemical co2 gas sensor." The Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=osu1073047249.
Full text
16
Kerman, Kian. "Ultra-thin solid oxide fuel cells: materials and devices." Thesis, Harvard University, 2014. http://dissertations.umi.com/gsas.harvard:11418.
Full textAbstract:
Solid oxide fuel cells are electrochemical energy conversion devices utilizing solid electrolytes transporting O2- that typically operate in the 800 - 1000 °C temperature range due to the large activation barrier for ionic transport. Reducing electrolyte thickness or increasing ionic conductivity can enable lower temperature operation for both stationary and portable applications. This thesis is focused on the fabrication of free standing ultrathin (<100 nm) oxide membranes of prototypical O2- conducting electrolytes, namely Y2O3-doped ZrO2 and Gd2O3-doped CeO2. Fabrication of such membranes requires an understanding of thin plate mechanics coupled with controllable thin film deposition processes. Integration of free standing membranes into proof-of-concept fuel cell devices necessitates ideal electrode assemblies as well as creative processing schemes to experimentally test devices in a high temperature dual environment chamber. We present a simple elastic model to determine stable buckling configurations for free standing oxide membranes. This guides the experimental methodology for Y2O3-doped ZrO2 film processing, which enables tunable internal stress in the films. Using these criteria, we fabricate robust Y2O3-doped ZrO2 membranes on Si and composite polymeric substrates by semiconductor and micro-machining processes, respectively. Fuel cell devices integrating these membranes with metallic electrodes are demonstrated to operate in the 300 - 500 °C range, exhibiting record performance at such temperatures. A model combining physical transport of electronic carriers in an insulating film and electrochemical aspects of transport is developed to determine the limits of performance enhancement expected via electrolyte thickness reduction. Free standing oxide heterostructures, i.e. electrolyte membrane and oxide electrodes, are demonstrated. Lastly, using Y2O3-doped ZrO2 and Gd2O3-doped CeO2, novel electrolyte fabrication schemes are explored to develop oxide alloys and nanoscale compositionally graded membranes that are thermomechanically robust and provide added interfacial functionality. The work in this thesis advances experimental state-of-the-art with respect to solid oxide fuel cell operation temperature, provides fundamental boundaries expected for ultrathin electrolytes, develops the ability to integrate highly dissimilar material (such as oxide-polymer) heterostructures, and introduces nanoscale compositionally graded electrolyte membranes that can lead to monolithic materials having multiple functionalities.Engineering and Applied Sciences
17
Mazri, Linda. "Nouveau procédé d’élimination des particules émises par les moteurs Diesel." Thesis, Lyon 1, 2011. http://www.theses.fr/2011LYO10037.
Full textAbstract:
L’objectif de cette étude était de développer une nouvelle génération de catalyseurs, dits électrochimiques, capables d’abaisser la température de régénération des filtres à particules, et de diminuer les coûts du post-traitement des moteurs Diesel, en évitant notamment une surconsommation en carburant. Pour cela, un banc de mesure a été développé où de forts moyens analytiques pour les phases gazeuses (GC et analyseur de NOx), particulaires (spectromètre de masse à aérosols AMS) et de caractérisations physiques des aérosols (SMPS, Scanning Mobility Particle Sizer) ont été couplés. Le catalyseur électrochimique développé est composé d’un catalyseur oxyde de type pérovskite La0.5Sr0.23Ag0.27MnO3±δ (noté LSAM), en contact avec un électrolyte solide conducteur par les ions O2-, la zircone dopée à l’oxyde d’yttrium (YSZ). L’enduction de ce catalyseur électrochimique directement dans les canaux d’un filtre à particule (FAP) en céramique (SiC) a montré des performances permettant d’abaisser la température de régénération des FAP de 100°C voire de 260°C selon le flux de régénération. Ces performances sont le résultat d’un effet de synergie entre les phases de la pérovskite LSAM et du conducteur ionique YSZThe aim of this study was to develop a new generation of catalysts, called electrochemical, which can lower the regeneration temperature of the particulate filter, and reduce post-treatment costs of Diesel engines, especially avoiding over-consumption of fuel. For this, a test bench has been developed where strong analytical analyzer for gas phases (GC and Nox analyzer), for particles (aerosol mass spectrometer AMS) and for physical characterization of aerosols (SMPS, Scanning Mobility Particle Sizer) have been coupled. The electrochemical catalyst developed is composed of a perovskite catalyst La0.5Sr0.23Ag0.27MnO3±δ (denoted LSAM), in contact with a solid electrolyte conductor by O2-ions, yttria stabilised zirconia (YSZ). The coating of the electrochemical catalyst directly into the channels of a particulate filter (DPF) showed performance to lower the DPF regeneration temperature of 100°C or even 260°C depending of the regeneration flow. These performances are the result of a synergistic effect between the phases of the perovskite LSAM and YSZ ionic conductor
18
Ray, Brian M. "A STUDY OF THE LITHIUM IONIC CONDUCTOR Li5La3Ta2O12: FROM SYNTHESIS THROUGH MATERIALS AND TRANSPORT CHARACTERIZATION." UKnowledge, 2014. http://uknowledge.uky.edu/physastron_etds/18.
Full textAbstract:
The ionic conductivity of the lithium ionic conductor, Li5La3Ta2O12, is studied in an attempt to better understand the intrinsic bulk ionic conductivity and extrinsic sample dependent contributions to the ionic conductivity, such as grain boundary effects and the electrode-electrolyte interface. To characterize the material, traditional AC impedance spectroscopy studies were performed as well novel in-situ nanoscale transport measurements. To perform the nanoscale measurements, higher quality samples were required and new synthesis techniques developed. The results of these new synthesis techniques was samples with higher densities, up to 96% of theoretical, and slightly higher room temperature ionic conductivity, 2x10^−5 S/cm. By combining the AC impedance spectroscopy results and in-situ nanoscale transport measurements from this study and prior reported results, as well as introducing models traditionally used to analyze supercapacitor systems, a new interpretation of the features seen in the AC impedance spectroscopy studies is presented. This new interpretation challenges the presence of Warburg Diffusion at low frequencies and the offers a new interpretation for the features that have been traditionally associated with grain boundary effects.
19
Alves, Fortunato Maíra. "La zircone yttriée : un nouveau support pour la catalyse environnementale." Thesis, Lyon 1, 2011. http://www.theses.fr/2011LYO10175.
Full textAbstract:
L'objectif de ce travail est l'étude des interactions entre des nanoparticules de platine et la zircone yttriée (YSZ pour Yttria-Stabilized Zirconia), oxyde conducteur ionique. Il s'agissait de transposer les effets de promotion électrochimique de la catalyse mis en évidence sur des films polarisés de platine de faible dispersion déposés sur des membranes denses de YSZ à des systèmes catalytiques conventionnels à base de nanoparticules métalliques dispersées sur des poudres de YSZ. La migration des ions oxydes promoteurs n'est plus contrôlée par une polarisation électrique mais induite thermiquement. Ces travaux ont permis de mettre au point une méthode de mesure de la dispersion du Pt déposé sur la zircone yttriée. Les interactions Pt/YSZ et notamment celles entre les lacunes d'oxygène de YSZ et les nanoparticules de Pt ont été étudiées par réduction en température programmée et spectroscopie infrarouge. L'importance des lacunes d'oxygène du support YSZ sur les propriétés de chimisorption du Pt et sur son activité catalytique pour l'oxydation du propane a été clairement montrée. La migration thermique des ions oxydes a été étudiée par échange isotopique 18O/16O. Un mécanisme de la réaction de combustion du propane a été proposé incluant le rôle prépondérant des oxydes de réseau de YSZ contrairement aux supports conventionnels en silice et en zircone non substituée. Finalement, les paramètres pouvant influencer les interactions Pt/YSZ comme la surface spécifique de YSZ, le taux d'oxyde d'yttrium, la méthode de préparation de YSZ ainsi que la teneur et la taille des nanoparticules de Pt ont été évalués. Les résultats ont mis en évidence la migration thermique des ions oxydes du support vers le Pt dès 100 °C. D'autre part, l'échange entre les oxygènes du réseau et ceux de la phase gaz est extrêmement rapide dès 100°C. L'activité catalytique du Pt semble promue par la mobilité des oxygènes du supportThe aim of this work is to investigate the interactions between Pt nanoparticles and Yttria-Stabilized Zirconia (YSZ), an ionically conducting support. The idea was to overcome the effects of electrochemical promotion of catalysis (EPOC) observed on Pt/YSZ electrochemical catalysts which present low metal dispersion to conventional catalytic systems based on metallic nanoparticles finely dispersed on YSZ powered support. In that configuration, the migration of the oxygen ions from YSZ toward the Pt surface is not electrically controlled but thermally induced without any polarisation. First, we have established a new procedure to measure the Pt dispersion over YSZ. The metal support interactions between Pt and YSZ were characterized by Temperature Programmed Reduction and Infrared Spectroscopy. The importance of the YSZ oxygen vacancies on the chemisorptive behaviours of Pt as well as its catalytic for the propane oxidation was clearly demonstrated. The thermal migration of oxygen ions was validated by using the Isotopic Exchange procedure 18O/16O. The impact of these vacancies was evaluated and a mechanism of the propane deep oxidation on Pt/YSZ was proposed including the important role of bulk YSZ oxygen species in opposition with conventional supports such as silica and non-substituted zirconia. Finally, the key parameters that can influence the Pt/YSZ interactions such as the YSZ specific surface area, the yttria content, the YSZ preparation route as well as the loading and size of Pt nanoparticles were investigated. Our results point out that the thermal migration of oxygen ions from YSZ toward Pt surface occurs from 100 °C. In addition, the exchange between oxygen species from YSZ bulk and those from the gas phase is extremely fast starting from 100 °C. The Pt catalytic activity for the propane deep oxidation seems to be promoted by the mobility of the bulk YSZ oxygen species
20
Howell, Thomas G. "Perovskites for use as sulfur tolerant anodes." University of Cincinnati / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1397467868.
Full text
21
Obeid, Emil. "Catalyseurs conducteurs ioniques pour l'oxydation des suies." Thesis, Lyon 1, 2013. http://www.theses.fr/2013LYO10150/document.
Full textAbstract:
Cette étude a pour finalité le développement d'une nouvelle famille de catalyseurs pour la combustion des suies Diesel afin de produire des filtres à particules (FAP) à régénération continue basse température. En effet, les régénérations périodiques des FAP actuellement commercialisés, engendrent une surconsommation plus ou moins élevée en carburant. Les catalyseurs étudiés sont des céramiques conductrices par les ions oxygènes et exempts de métal noble. L'ensemble de ces études a permis d'aboutir à plusieurs conclusions majeures. Les oxygènes actifs pour oxyder les particules de suies à basse température sont les oxygènes contenus dans le catalyseur. L'oxydation de la suie a donc lieu à l'interface solide/solide : suie/catalyseur. Un mécanisme de type électrochimique comme dans une pile à combustible mais à l'échelle nanométrique a été proposé : l'oxydation de la suie représente la réaction anodique qui se déroule aux points de contact suie / 8-YSZ, les électrons produits diffusent à travers les particules de suie vers les point triples entre les particules de suie (conductrices électroniques), la phase gaz (présence d'oxygène) et 8-YSZ (conducteur ionique) où se déroule la réaction cathodique d'incorporation de l'oxygène gazeux dans le matériau. Les paramètres clés qui gouvernent l'activité catalytique sont la surface de contact suie/catalyseur et donc la granulométrie de la poudre de catalyseur ainsi que la pression partielle d'oxygène dans la phase gaz et la mobilité de l'oxygène dans le catalyseurThis study aims to develop a new family of catalysts for diesel soot combustion to produce and optimize self-DPFs, based on ionic conducting ceramics, able to continuously burn soot particulates at low temperatures without fuel overconsumption and without the use of noble metals. The investigated catalysts are oxygen ionically conducting ceramics. Yttria stabilized Zirconia (8-YSZ containing 8 mol% of yttria) was chosen as the reference catalyst due to its high thermal and chemical stability and good ionic conductivity. A set of experiments was implemented to vary different parameters that can influence the reactivity of the reference catalyst. All of these studies have resulted in several major conclusions. Oxygen species active to oxidize soot particles at low temperature are those contained in the catalyst. An electrochemical type mechanism as in a fuel cell but at the nanoscale was proposed: the soot oxidation represents the anodic reaction which occurs at the contact points soot / 8-YSZ/O2 (gas) electrons are diffused through soot particles to triple points between the soot particles (electronic conductor), the gas phase (presence of oxygen) and 8-YSZ (ion conductor) where the cathodic reaction takes place with the incorporation of gaseous oxygen into the ceramic. The key parameters that influence the catalytic activity of 8-YSZ are soot / catalyst contact and thus the agglomerates size of the catalyst powder, the oxygen partial pressure in the gas phase and the mobility of oxygen in the catalyst
22
Lecavelier, des Etangs-Levallois Hervé. "Etude par résonance magnétique nucléaire des mouvements ioniques et électroniques dans un polymère conducteur : le polypyrrole." Grenoble 1, 1986. http://www.theses.fr/1986GRE10125.
Full textAbstract:
Mouvements ioniques sondes par la resonance des spins nucleaires du fluor des ions bf::(4)**(-) et analyse par les variations thermiques du second moment et du temps de relaxation du fluor. Dynamique des spins electroniques
23
Trupkovic, Alexandra. "Etude de verres borates de lithium utilisables dans les microbatteries : corrélation conductivité ionique / propriétés thermomécaniques." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2009. http://tel.archives-ouvertes.fr/tel-00659229.
Full textAbstract:
L'utilisation croissante de systèmes électroniques miniaturisés induit une forte demande en microsources d'énergie performantes, telles que les microbatteries au lithium. En vue d'améliorer les propriétés de l'électrolyte, nous avons étudié les propriétés électriques et thermomécaniques d'électrolytes solides de type borate de lithium. Une corrélation entre la conductivité ionique et le coefficient de dilatation thermique (CTE) a été mise en évidence pour différentes compositions de verres massifs. A partir des résultats de CTE obtenus, un modèle de prédiction basé sur les travaux de Appen permettant la détermination de ce dernier en fonction de la composition chimique a été développé. Dans un second temps, différentes techniques de préparation de cibles denses nitrurées ont été mises en œuvre afin d'abaisser le CTE de la cible et ainsi permettre son utilisation sur une plus longue durée. Par ailleurs, l'utilisation d'une cible nitrurée a également été envisagée pour augmenter la teneur en azote dans les couches minces. Finalement, des couches minces d'électrolyte de différentes compositions ont été préparées par pulvérisation cathodique (sous plasma d'argon ou d'azote pur) et ont fait l'objet d'une caractérisation chimique, structurale, électrique et thermomécanique. Le rôle bénéfique de l'azote sur la conductivité ionique des couches minces a ainsi pu être confirmé.
24
Palácio, Gustavo. "Conducteurs ioniques transparents et matériaux fluorescents à base de mélanges hybrides PEO/PPO-Siloxane." Thesis, Université Clermont Auvergne (2017-2020), 2017. http://www.theses.fr/2017CLFAC075/document.
Full textAbstract:
Ce travail de thèse présente une méthode de synthèse par le procédé sol-gel pour la préparation de matériaux hybrides organiques-inorganiques (OIH) basés sur le mélange de deux polyéthers différents, le poly (oxyde d´éthylène) (PEO) et le poly (oxyde de propylène) (PPO) liées de façon covalente avec l´agent de réticulation ureasil (U). Dû aux différents sites actifs présents dans la structure du matériau OIH, plusieurs cations métalliques peuvent être introduits dans la matrice hybride par complexation soit avec l´oxygène de type éther, soit avec l´oxygène du type carbonyle. Suite à ce constat, différentes matrices hybrides ont été synthétisées en introduisant des ions Eu3+ ou Li+ afin de conférer aux matériaux des propriétés optiques ou électriques. La compréhension des propriétés structurales et thermiques des différents polymères, l´ajout de différents cations Eu3+/Li+, et l'effet du plastifiant (PPO2000) dans la mélange hybride U-xPEO1900:/U-1-xPPO2000 (ratio de PPO2000 dans la mélange, x = 0.2, 0.5 et 0.8), ont été étudiés par DSC et SAXS. Les résultats de DSC ont révélé une unique température de transition vitreuse (Tg) pour tous les matériaux étudiés. L´ajout des ions Eu3+ dans le matrice n´a pas causé de variations dans les valeurs de Tg tandis que l´insertion de cations Li+ a provoqué une augmentation dans les valeurs de Tg, indiquant l´existence d’interactions entre les cations Li+ et la phase polymérique du matériau OIH. Les courbes de calorimètrie de l´U-PEO1900 ont aussi révélé la présence d´une pic endothermique à 25 °C, associé à la fusion des domaines cristallins du PEO1900. La présence d´un deuxième maximum dans les courbes de diffusion des rayons X à petits angles (SAXS) a confirmé l’existence de la structure semi-cristalline du PEO1900 dans une région de température entre -100 °C < T < Tf. Tous les échantillons, non-dopés et dopés avec les ions Li+ et Eu3+, ont montré un pic de corrélation indiquant que la nano-structure de la matrice hybride n´est pas affecté par le dopage avec les cations métalliques. Les études par Spectroscopie Infrarouge à Transformée de Fourier (FTIR) et par spectroscopie Raman ont confirmé l´interaction des ions Eu3+ avec l´oxygène du type carbonyle présent dans les groupes urées de la matrice hybride, et des ions Li+ avec l´oxygène du type éther. La photodégradation accélérée a révélé une perte des performances de la photo-luminescence (PL) associée à des changements dans la coordination des ions Eu3+ avec la matrice hybride. La photodégradation induit la formation de photo-produits venant de la β-scission du macroradical formé dans la portion organique de la matrice hybride. La β-scission peut-être responsable pour la diminution de la PL du matériau dû la perte de l´efficacité de l´effet antenne du ligand organique pour le centre luminescent. La transition dans la région visible du rouge vers le bleu avec la photodégradation qualifie ces matériaux de bons candidats pour l'application comme capteurs et marqueurs optiques. La conduction ionique des matrices hybrides dopés avec Li+ a été évaluée par Spectroscopie d´Impédance en fonction de la température et les résultats ont révélé des corrélations entre la superstructure lamellaire du PEO1900 et le mécanisme de conduction. L´addition d´un plastifiant, le PPO2000, a permis l´augmentation de la conductivité ionique dans une région de température entre -100 °C < T < 10 °C dû à l´augmentation de la portion amorphe utilisée comme chemin de transport ionique efficace dans le mélange polymère hybride U-xPEO1900/U-1-xPPO2000In this PhD thesis a greener synthesis route via sol-gel reactions aiming to prepare multifunctional organic-inorganic hybrid (OIH) materials based on blending of two polyether amine end chains (i.e., Jeffamine® compounds) Poly(ethylene oxide) (PEO) and Poly(propylene oxide) (PPO) covalently bonded with an ureasil cross-linking agent (U) is reported. Due to the different polar oxygen sites present in this OIH material, several metallic cations can to be introduced into the OIH matrix via ether- or carbonyl-type oxygen. So, different OIH matrices containing Eu3+ or Li+ cations were synthetized to evaluate their potential as photoluminescent or ionic conductor material, respectively. The thermal and structural characteristics of the Eu3+ or Li+ – loaded OIH materials, as well as the plasticizer effect of PPO2000 at the U-xPPO2000:/U-1-xPEO1900, (PPO2000 fraction x = 0.2, 0.5 and 0.8) blends, were carried out by DSC and SAXS. DSC results revealed a unique glass transition temperature (Tg) for all the studied OIH materials. The addition of Eu3+ cations do not change the Tg values while the Li+ cations caused an increase in the values of Tg, due to the Li+ interaction with the polymeric phase of the material. The U-PEO1900 calorimetric curves also showed the presence of an endothermic peak at 25 °C associated to the fusion of the crystalline domains of PEO1900. The second maxima observed in the curves of small angle X-ray scattering (SAXS) confirmed the presence of the crystalline structure of PEO1900 in a temperature range of -100 < T < Tf. All the samples, undoped and Li+ or Eu3+ doped ones, showed a correlation peak indicating that the OIH nano-structure is not affected by the metallic cations doping. Analysis carried out by Fourier Transform InfraRed (FTIR) and Raman Spectroscopy confirmed the Eu3+ cations interaction via the oxygen carbonyl-type present in the urea groups of the hybrid matrix, and that of Li+ cations with the oxygen ether-type. The accelerate photo-degradation revealed a loss of the photo-luminescence (PL) efficiency due to the changes in the Eu3+ cations coordination with the hybrid matrix. The photo-degradation induces the formation of photo-products from the macro-radical β-scission formed in the organic fraction of the hybrid matrix. The β-scission can be responsible for the material PL decrease due to the drop in the antenna effect from organic ligand to luminescent center. The visible emission transition from red → blue with the photo-degradation qualify these materials as good candidates to be applied as sensors and optical markers. The ionic conduction of the Li+-loaded hybrid matrices was investigated by Impedance Spectroscopy as a function of the temperature. Results showed a correlation between the lamellar superstructure of the PEO1900 and the conducting process. The plasticizers addition (PPO2000) alloyed to improve the value of the ionic conductivity in the low temperature range, -100 °C < T < 10 °C due to the increase of the amorphous fraction used as effective ionic transport pathway in the U-xPEO1900/U-1-xPPO2000 polymeric hybrid blend
25
Hadjar, Abdelkader. "Catalyseurs électrochimiques pour le stockage et la réduction des oxydes d'azote (NOx)." Thesis, Lyon 1, 2009. http://www.theses.fr/2009LYO10111.
Full textAbstract:
L’objectif de ce travail était de démontrer la possibilité de coupler sur un même catalyseur, la fonction de stockage et réduction des NOx (sur le baryum) avec un effet électrochimique reposant sur un système micropile. Ce système micropile est composé de nanoparticules catalytiques (Pt et Rh) déposés sur conducteur ionique par les ions O2- (YSZ) en contact avec un support conducteur électronique (SiC dopé) de façon à pouvoir générer, sous mélanges réactionnels, une force électromotrice capable de réduire électrochimiquement une partie des NOx sur le Pt et d’oxyder le CO, les hydrocarbures imbrûlés et H2 sur le Rh. L’effet micropile a été observé sur un catalyseur Pt/Ba (matériau de stockage)/YSZ/Rh enduit dans les canaux d’un filtre à particule en carbure de silicium dopé, en condition essence pauvre à 400°C et en condition Diesel à plus basse température (300°C). Une augmentation de la conversion des NOx d’environ 10% a été observé sur les catalyseurs micropile. L’effet électrochimique a été détecté par une surproduction de CO2, en milieu riche (très peu ou pas de O2) provenant de la réaction d’oxydation électrochimique du CO (produit par vaporeformage) en réagissant avec les ions O2- provenant de YSZ. De plus, des tests catalytiques ont montré que YSZ peut être utilisée comme matériau de stockage des NOx. En effet, un traitement réducteur préalable augmente fortement sa capacité de stockage des NOxThe main objective of this study was to demonstrate the coupling between NOx storage/reduction process on barium, with an electrochemical reduction of NOx (micro fuel cell effect) on the same catalyst. The micro fuel cell effect is ensured by a an electromotive force (potential) which is created between catalytic nanoparticules (Pt and Rh) in contact with an ionic conductor (YSZ) and an electronic conductor (doped SiC). The micro fuel cell effect was observed, during the regeneration phase of the catalysts (rich period), on a Pt/Ba/doped α-SiC-YSZ/Rh monolithic system under lean-burn gasoline conditions at 400°C with an enhancement of about 10 % of the NOx conversion over a complete cycle lean/rich. This electrochemical effect was characterized by the electrochemical oxidation of CO (produced by steam reforming) into CO2 by using O2- ions coming from YSZ. Under Diesel conditions, the micro fuel cell system was found to work at low temperature especially at 300°C. In the second part of the work, a new generation of NOx Storage and reduction catalyst was developed consisting only of noble metals (Pt and/or Rh) deposited on YSZ support (Ba free catalyst). The catalytic measurements revealed that YSZ can be used as a NOx storage material in lean burn conditions (Gasoline and Diesel) especially when it was previously reduced under hydrogen. The storage mechanism would take place on the oxygen vacancies created by the removal of O-2 ions from the YSZ structure
26
Guggilla, Srinivas. "Synthesis and characterization of Perovskite-related ionic and mixed ionic-electronic conductors /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
Full text
27
Mackenzie, Margaret A. "Mechanisms of ionic conduction in glass." Thesis, University of Aberdeen, 1987. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU499561.
Full textAbstract:
The effect on conductivity of progressively substituting foreign alkali for host alkali in a series of lithium aluminoborate glasses has been studied. The shape of the conductivity isotherm in the dilute foreign alkali region was found to be the same for both Na+ and K+ dopants. Assuming a 'regular interstitialcy model' for ionic conduction conductivity data for a variety of glasses were subjected to isothermal analysis, allowing concentrations of mobile species and mobilities to be calculated. Conductivity changes were found to be largely attributable to changes in mobility, the concentration term remaining remarkably constant. The a.c. behaviour of aluminoborate glasses has also been studied and modulus spectra fitted using the Kohlrausch-Williams-Watts function for various beta-values. Decreasing the total alkali content and substituting foreign alkali for host alkali was observed to cause some narrowing of the modulus, mixed-alkali glasses behaving much as though only 'host' cations were present. 'Microscopic' activation energies (E_a) have been calculated from beta-values (Ea=beta Ead.c.). These are found to follow the trend in experimentally observed activation energies indicating that the mixed alkali effect occurs as the result of decreases in both long- and short-range ionic mobilities. A cluster-bypass model has been proposed in an attempt to reconcile the above results. The model assumes that the mobile species are to be found in a tissue material surrounding the clusters. A brief examination of the site preferences of spectroscopic probe ions (T1+ and Pb2+) in mixed cation glasses by u.v. spectroscopy indicated a dependence of the frequency of the absorption band on the reagents used in glass preparation. This result is thought to point towards some structural effects persisting in the melt which in turn may be important with respect to cluster formation in the glass.
28
Chen, Guannan. "Mixed ionic-electronic conductors in gas separation applications." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/mixed-ionicelectronic-conductors-in-gas-separation-applications(02fdfa3c-f388-453d-85c4-b2f295d59295).html.
Full textAbstract:
Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) and SrCo0.48Fe0.12Ti0.4O3-delta (SCFT) were synthesised by co-precipitation. BSCF was pressed and sintered at 1100℃ for 10 hours to pellets (relative density: 93%) from which X-ray diffraction (XRD) revealed single Pm-3m phase (a=3.9782 A). Scanning electron microscopy (SEM) revealed clear equiaxed grains (grain size 33 ± 16 micro metre). The pellets were decomposed in 7 ± 1 % CO2/N2 at 800℃ for 1 to 30 minutes. XRD confirmed secondary phases: R-3mH phase (a=b=5.1397 A, c=9.4847 A) and Fm-3m phase (a=4.2490 A). Electron backscattered diffraction (EBSD) ascribed R-3mH and Fm-3m phases to the surface and part of the cross-section precipitates, respectively as revealed by SEM. Energy dispersive X-ray spectroscopy (EDX) revealed the compositions of R-3mH and Fm-3m phases to be Ba0.65±0.03Sr0.35±0.03CO3 (BSC) and CoO, respectively. Transmission electron microscopy (TEM) and EDX revealed the structure (15R, R3m and R-3mH) and composition (Ba0.20Sr0.10Co0.59Fe0.10Ox) of lamellar precipitates in cross-section, suggesting Ba and Sr diffuse from the lamellae to BSC. A unique orientation relation (BSCF {111} // BSC {0001}) was uncovered by EBSD. TEM revealed high symmetry contact planes of lamellae and BSCF, suggesting nucleation energy governs decomposition. Fresh BSCF pellets were decomposed in N2 at 800℃. Fm-3m and P63/mmc phases were confirmed by XRD and lamellae were observed by SEM, followed by decomposition in 7±1 % N2/CO2 at 800℃. XRD revealed higher weight % of BSC and CoO. SEM revealed BSC preferring lamellae, hence hexagonal phases accelerated BSC formation. BSCF pellets were dip coated in SCFT propan-2-ol suspension (3:10), followed by sintering at 1165℃ for 10 hours. XRD revealed a Pm-3m phase (a=3.885 A) and SEM revealed a grain size of 65 ± 9 micro metre and open porosity of 1.6 ± 1 %. They were annealed in 7 ± 1 % CO2/N2 at 800℃. XRD revealed no secondary phases, suggesting enhanced stability. However, oxygen permeability was reduced (1.2 ml/cm2 to 0.8 ml/cm2) because the coating composition changed to Ba0.20Sr0.27Co0.40Fe0.10Ti0.04Ox; this was revealed by EDX.
29
Pacheco, Moreno Celia Maria. "Organic mixed ionic/electronic conductors for bioelectronics applications." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/49790.
Full textAbstract:
The bioelectronics field has incorporated an increasing variety of conducting polymers in applications that involve mixed ionic/electronic transport, yet there is still a lack of design rules to purposefully tune the electronic and ionic contributions to a material's conductivity, as well as processing methods to further control and understand their interplay. New undoped co-polymers were explored as electroactive materials in aqueous media. The range of materials allowed establishing a simple design rule with potential to be explored in other model semiconductors. The most hydrophilic system showed promising response when benchmarked with poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) in order to be employed in new operation modes of devices which rely on the electrochemical doping of the active layer, such as organic electrochemical transistors (OECTs). The capabilities of the most promising system were further exploited as an ion-to-electron converter by creating multicomponent systems that included a polar insulator to tune their ionic transport. The straight-forward and chemically inert blending approach showed enhanced transport of ionic species while maintaining their electronic transport as well as displaying characteristic response times linked to the presence of the polar phase. By using the semiconductor as a model system and controlling the volume of aggregates present in the solid-state by means of processing, a phenomenological description was given of ionic transport in different regions of semicrystalline polymers along with their associated decay rates. Finally, the effect of humidity in the charge transport of the undoped co-polymers was explored, with a focus on elucidating ionic contributions from electronic ones. The incorporation of a ionic conductor, Nafion, in a bilayer structure was explored and showed an intimate interaction between the proton conductor and the electronic conductor. The potential of the multilayer structures as humidity sensors and other remarkable features found in their charge transport make these promising systems for further applications in bioelectronics.
30
Mattos, Ritamara Isis de. "Estudo de condutores protônicos a base de macromoléculas naturais." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-25092011-171004/.
Full textAbstract:
Esta tese apresenta os resultados do estudo de eletrólitos poliméricos protônicos obtidos a base de gelatina e quitosana, modificadas através da adição de glicerol e formaldeído - ácidos acético ou clorídrico foram adicionados para promover a condutividade iônica dos filmes. Foram também preparadas blendas a partir de gelatina com quitosana, assim como filmes a base de gelatina e nanopartículas. Com exceção dos filmes com nanopartículas, todos eles possuem boa transparência, estabilidade térmica, maleabilidade, aderência ao vidro e apresentam uma superfície homogênea, sem trincas ou rachaduras. As temperaturas de transição vítrea (Tg) dos eletrólitos foram obtidas do estreitamento de linha de RMN. A taxa de relaxação spin-rede do \'ANTPOT. 1 H\' em função da temperatura mostrou um máximo bem definido cuja posição depende da concentração de ácido no caso da gelatina e da quantidade de glicerol no caso da quitosana, refletindo a alta mobilidade do próton nestes eletrólitos. As técnicas de RPE, onda contínua e pulsada, foram utilizadas para o estudo de eletrólitos dopados com \'CU\'CL\'O IND.4\'. Os valores de condutividade iônica dos eletrólitos são da ordem de \'10 POT.-5\' S/cm para os filmes de gelatina (com ácido acético ou clorídrico), quitosana e blendas e entre \'10 POT.-6\' a \'10 POT.-8\' para os eletrólitos de gelatina com nanopartículas. Estes estudos revelaram que a concentração de ácido acético ou clorídrico (na gelatina), influencia a condutividade iônica dos eletrólitos, mas, para o caso das blendas esta influência é pequena. No caso dos filmes de gelatina com nanopartículas, a condutividade diminui de forma significativa. Em relação aos eletrólitos de quitosana a condutividade iônica é influenciada pela quantidade de glicerol adicionado. Verificou-se que o aumento da temperatura até 80°C promove o aumento da condutividade iônica para todos os filmes estudados.This thesis shows the results from the study of protonic polymer electrolytes obtained from gelatin and chitosan, modified by the addition of glycerol and formaldehyde - acetic and hydrochloric acids are added to promote the ionic conductivity of the films. Blends based on chitosan and gelatin were also prepared, as well as films based on gelatin and nanoparticles. With the exception of the films with nanoparticles, all samples presented good transparency, thermal stability, flexibility, adhesion to glass and homogeneous surface without cracks. The glass transition temperature (Tg) of the electrolytes were obtained from the NMR line narrowing. The spin-lattice relaxation rate of the \'ANTPOT. 1 H\' spin-network as a function of temperature showed a well-defined maximum whose position depends on the concentration of acid in the case of gelatin and on the glycerol content in the case of chitosan, reflecting the high mobility of the protons in the electrolytes. Continuous wave and pulsed EPR techniques were used to study the electrolytes doped with \'CU\'CL\'O IND.4\'. The values of the ionic conductivity of the electrolytes are of the order of \'10 POT.-5\' S/cm for the films of gelatin (with acetic or hydrochloric acids), chitosan and blends and from \'10 POT.-6\' to \'10 POT.-8\' for the electrolytes of gelatin with nanoparticles. These studies revealed that the concentration of acetic or hydrochloric acids (in gelatin), influences the ionic conductivity of the electrolytes but, in the case of blends, this influence is small. In the case of the films based on gelatin with nanoparticles, the ionic conductivity decreases significantly. In relation to the electrolyte based on chitosan, the ionic conductivity is influenced by the amount of glycerol added. It was found that increasing the temperature to 80°C promotes the increase of ionic conductivity for all films studied.
31
O'Sullivan, Kevin F. "The Raman spectra of simple ionic systems." Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.258149.
Full text
32
Bhatt, Dipali M. "Ionic conduction of thin films of polymer electrolytes." Thesis, University of Sheffield, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298880.
Full text
33
Düvel, A., C. V. Chandran, and Paul Heitjans. "Mixed Ionic Conduction in Nano- and Microcrystalline BaLiF3." Diffusion fundamentals 21 (2014) 29, S.1-2, 2014. https://ul.qucosa.de/id/qucosa%3A32439.
Full text
34
Karlsson, Christian. "Ionic conduction in glasses and nanocomposite polymer electrolytes /." Göteborg : Chalmers university of technology, 2003. http://catalogue.bnf.fr/ark:/12148/cb392991306.
Full text
35
Mokkelbost, Tommy. "Synthesis and Characterization of CeO2- and LaNbO4-based Ionic Conductors." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2006. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-1762.
Full textAbstract:
Ceramic electrolytes that conduct either oxygen ions or protons at intermediate temperatures are important materials for use in e.g. solid oxide fuel cells, the prime candidate to produce electricity by electrochemical reactions. There are still challenges with respect to the cell performance which have to be solved before solid oxide fuel cells become a commercial success. One of the main topics in this field concerns the enhancement of ionic conductivity at suitable operation temperatures. During the last decade nanocrystalline materials have received considerable attention. Nanocrystalline ionic conductors may have higher ionic conductivity compared to traditional ceramics with grain sizes in the micrometer range. The aim of this work has been to develop electrolyte ceramic materials with a designed microstructure. CeO2- and LaNbO4-based materials have been prepared through a complete route, from preparation of powders to densification of ceramics including characterization of selected properties. CeO2-based materials are oxygen ion conductors and show higher ionic conductivity compared to the more common yttria stabilized zirconia (YSZ), thus a lower operation temperature is possible. LaNbO4-based materials have recently been suggested as a promising proton conductor stable in CO2/H2O atmosphere. In Paper I, powder synthesis of nanocrystalline CeO2-based powders (CeO2, Ce0.8Gd0.2O1.9 and Ce0.8Sm0.2O1.9) using combustion synthesis with glycine as fuel and nitrate as oxidizer is reported. The influence of glycine to nitrate (G/N) ratio on the pure CeO2-based powders was investigated. The influence of calcination temperature on crystallite size, surface area and carbonate species remaining from combustion reaction was studied, with special attention to powders prepared using a near-stoichiometric G/N-ratio. A G/N-ratio of 0.55 and calcination at 550°C in oxygen flow resulted in high quality powders with a crystallite size of ~10 nm with low degree of agglomeration due to the vigorous combustion. The G/N-ratio influenced the densification behavior of the powders. A G/N-ratio of 0.55 resulted in excellent sintering properties with an onset of sintering at ~600°C and fully dense materials were obtained at ~1300°C. In Paper II, three different sintering techniques have been used to prepare dense (>95%) CeO2-based materials from the high-quality powders described in Paper I: Spark plasma sintering, hot pressing and conventional sintering. The three different sintering techniques resulted in different grain sizes, ranging from 160 nm by spark plasma sintering, to 50 μm by conventional sintering mainly due to difference in sintering temperature and the applied pressure. The materials were reduced after hot pressing and a minor reduction was observed after spark plasma sintering. The materials were easily reoxidized at temperatures above 200°C. The electrical conductivity, measured by van der Pauw method, revealed no clear dependence on grain size, but instead a dependence on the sintering method used. The substituted materials prepared by hot pressing had a lower electrical conductivity and higher activation energy compared to the materials prepared by both conventional and spark plasma sintering. Thus, it is proposed that the reduction of Ce observed during hot pressing might be detrimental for the ionic conductivity even after reoxidation. Hardness and fracture toughness, measured by Vickers indentation, were more influenced by chemical composition than the grain size of the materials. Higher fracture toughness and lower hardness were observed for pure CeO2 compared to the substituted materials. A novel route to prepare large quantity of sub-micron LaNbO4-based powders by spray pyrolysis is presented in Paper III. An aqueous solution containing stable La-EDTA complex and Nb-malic acid complex was spray pyrolysed using an in-house spray pyrolysis unit. The pure, nonagglomerated powders had a particle size of ~0.1 μm, narrow particle size distribution and high purity after calcination at 800°C. The sintering behavior, microstructure, phase content and electrical conductivity of La1-xAxNbO4 (x = 0, 0.005 and 0.02 and A = Ca, Sr and Ba) prepared by spray pyrolysis is presented in Paper IV. The powders had excellent sintering properties and achieved high density after conventional sintering at 1200°C or as low as 1050°C by hot pressing at 25 MPa. A grain size down to 0.4 μm was achieved by hot pressing. The acceptor doped materials had a more homogenous microstructure due to secondary phases inhibiting grain growth compared to pure LaNbO4. Liquid secondary phase was formed at elevated temperatures in acceptor doped LaNbO4, resulting in tremendous grain growth (~70 μm) and microcracking in La0.98Ba0.02NbO4. The solubility of Sr on La-site in LaNbO4 was determined to 1% at 1500°C, and similar low solubility of CaO and BaO in LaNbO4 was inferred. Protons were found to be the main charge carrier up to 1000°C in wet hydrogen. Higher grain boundary resistivity was observed compared to previous work, possibly due to lower sintering temperature resulting in secondary phases due to lower solubility of AO. The thermal and mechanical properties of LaNbO4-based materials are presented in Paper V. The materials possessed a ferroelastic to paraelastic phase transition at ~500°C and the linear thermal expansion was significant lower for the paraelastic compared to the ferroelastic phase. The pure LaNbO4 had a significantly lower hardness compared to acceptor doped (Ca, Sr and Ba) LaNbO4 due to large grain size and microcracking. The fracture toughness of La0.98Sr0.02NbO4, measured by SEVNB method, was 1.7±0.2 MPa·m1/2. The ferroelastic properties were confirmed by non-linear stress-strain relationship and remnant strain. The remnant strain decreases with increasing temperature and increasing acceptor doping. The latter was possibly due to secondary phases pinning the ferroelastic domain boundaries.
36
Guan, Jie. "Ceramic membranes of mixed ionic-electronic conductors for hydrogen separation." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/19423.
Full text
37
Li, Cheng. "Structural, surface and electrochemical studies of LaNbO4 based ionic conductors." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/54387.
Full textAbstract:
In the search for novel solid oxide fuel cell (SOFC) electrolytes, research focus has shifted from conventional materials with high symmetry fluorite and perovskite structures, to those structures with anisotropic conducting paths and defective local environment. Amongst the novel fast ion conductors are the hyperstoichiometric modulated CeNbO4+d phases, which have displayed remarkably oxygen diffusivity in the intermediate temperature region (500 °C to 750 °C). The oxidation of Ce3+ to Ce4+, however, leads to undesirable electronic conduction. In addition, the structure and conducting mechanism of the modulated fergusonite phases has been left unexplored due to the structural modulation. This work thus aims to investigate the crystal structure, phase evolution and transport properties of LaNb1-xWxO4+d, a structural analogue to CeNbO4.25. The hyperstoichiometric LaNb1-xWxO4+d phases (x = 0.08–0.16) adopt a (3 + 2)D modulated structure, with cation ordering at the Nb/W site. Using the superspace group I2/c(α1,0,γ1)00(α2,0,γ2)00, the room temperature crystal structure of LaNb0.88W0.12O4+d has been refined using the Rietveld method with powder synchrotron diffraction data. The refined structure model suggests extended B-site coordination numbers, ranging from 6 to 8 with a 3Å cut-off. The additional B-O bonds accommodate the variations in local environment and provide linkages between the NbOx slabs, forming a 3D network similar to that in CeNbO4.25. In situ neutron diffraction has revealed a sequence of structural transformations which has been overlooked in the literature. Compared with the undoped LaNbO4, the conductivity of LaNb1-xWxO4+d phases is much improved, reaching 8 × 10-3 S cm-1 at 863 °C for LaNb0.88W0.12O4+d. 18O tracer diffusivity measurements have confirmed oxygen ions being the major charge carriers, and an interstitial conducting mechanism has been proposed to explain the improved conductivity. Despite the huge interest of utilising LaNbO4 based materials for SOFC electrolyte application, their surface chemistry, which plays an important role in determining electrochemical performance, has been left unexplored. Surface chemistry of acceptor doped LaNbO4 is investigated using LEIS and SIMS. A Nb and Sr enriched surface layer, approximately 6–7 nm thick, has been identified after annealing La0.99Sr0.01NbO4-d at 1000 °C. Isotopic exchange experiments reveal a systematic decrease in isotopic surface concentration after the Sr enriched layer has developed at the surface, highlighting the impact of surface chemistry on the ion transport process.
38
Bu, Junfu. "Advanced BaZrO3-BaCeO3 Based Proton Conductors Used for Intermediate Temperature Solid Oxide Fuel Cells (ITSOFCs)." Doctoral thesis, KTH, Tillämpad processmetallurgi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-165073.
Full textAbstract:
In this thesis, the focus is on studying BaZrO3-BaCeO3 based proton conductors due to that they represent very promising proton conductors to be used for Intermediate Temperature Solid Oxide Fuel Cells (ITSOFCs). Here, dense BaZr0.5Ce0.3Y0.2O3-δ (BZCY532) ceramics were selected as the major studied materials. These ceramics were prepared by different sintering methods and doping strategies. Based on achieved results, the thesis work can simply be divided into the following parts: 1) An improved synthesis method, which included a water-based milling procedure followed by a freeze-drying post-processing, was presented. A lowered calcination and sintering temperature for a Hf0.7Y0.3O2-δ (YSH) compound was achieved. The value of the relative density in this work was higher than previously reported data. It is also concluded that this improved method can be used for mass-production of ceramics. 2) As the solid-state reactive sintering (SSRS) represent a cost-effective sintering method, the sintering behaviors of proton conductors BaZrxCe0.8-xLn0.2O3-δ (x = 0.8, 0.5, 0.1; Ln = Y, Sm, Gd, Dy) during the SSRS process were investigated. According to the obtained results, it was found that the sintering temperature will decrease, when the Ce content increases from 0 (BZCLn802) to 0.3 (BZCLn532) and 0.7 (BZCLn172). Moreover, the radii of the dopant ions similar to the radii of Zr4+ or Ce4+ ions show a better sinterability. This means that it is possible to obtain dense ceramics at a lower temperature. Moreover, the conductivities of dense BZCLn532 ceramics were determined. The conductivity data indicate that dense BZCY532 ceramics are good candidates as either oxygen ion conductors or proton conductors used for ITSOFCs. 3) The effect of NiO on the sintering behaviors, morphologies and conductivities of BZCY532 based electrolytes were systematically investigated. According to the achieved results, it can be concluded that the dense BZCY532B ceramics (NiO was added during ball-milling before a powder mixture calcination) show an enhanced oxygen and proton conductivity. Also, that BZCY532A (NiO was added after a powder mixture calcination) and BZCY532N (No NiO was added in the whole preparation procedures) showed lower values. In addition, dense BZCY532B and BZCY532N ceramics showed only small electronic conductivities, when the testing temperature was lower than 800 ℃. However, the BZCY532A ceramics revealed an obvious electronic conduction, when they were tested in the range of 600 ℃ to 800 ℃. Therefore, it is preferable to add the NiO powder during the BZCY532 powder preparation, which can lower the sintering temperature and also increase the conductivity. 4) Dense BZCY532 ceramics were successfully prepared by using the Spark Plasma Sintering (SPS) method at a temperature of 1350 ℃ with a holding time of 5 min. It was found that a lower sintering temperature (< 1400 ℃) and a very fast cooling rate (> 200 ℃/min) are two key parameters to prepare dense BZCY532 ceramics. These results confirm that the SPS technique represents a feasible and cost-effective sintering method to prepare dense Ce-containing BaZrO3-BaCeO3 based proton conductors. 5) Finally, a preliminary study for preparation of Ce0.8Sm0.2O2-δ (SDC) and BZCY532 basedcomposite electrolytes was carried out. The novel SDC-BZCY532 based composite electrolytes were prepared by using the powder mixing and co-sintering method. The sintering behaviors, morphologies and ionic conductivities of the composite electrolytes were investigated. The obtained results show that the composite electrolyte with a composition of 60SDC-40BZCY532 has the highest conductivity. In contrast, the composite electrolyte with a composition of 40SDC-60BZCY532 shows the lowest conductivity. In summary, the results show that BaZrO3-BaCeO3 based proton-conducting ceramic materials represent very promising materials for future ITSOFCs electrolyte applications.QC 20150423
39
Wu, Zhonglin. "Mixed ionic-electronic conductors for electrodes of barium cerate based SOFCs." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/19979.
Full text
40
Zachariah, Manesh. "Electronic & ionic conduction & correlated dielectric relaxations in molecular solids." Doctoral thesis, Universitat Politècnica de Catalunya, 2016. http://hdl.handle.net/10803/404446.
Full textAbstract:
The study of crystalline materials has played a prominent role in solid state physics, whose basic theories were formulated for crystalline matter. However, disordered materials are more abundant in nature than crystalline ones, and, moreover, many practical applications use materials which are weakly or strongly disordered, such as molecular crystals, glasses, plastic crystals, liquids, polymers, or liquid crystals. In glasses, for example, the arrangement of the constituent atoms or molecules lacks any long-range order. From a fundamental viewpoint, we still lack an understanding of the properties of disordered materials and of the glass transition: understanding the many fascinating issues related with disorder requires in fact the use of concepts that are far from the well-known solid-state concepts associated with periodicity. From an applied perspective, the intense research in disordered solids is driven by the technological importance of these materials in daily life. From an electrical viewpoint, disordered solids can conduct electricity by transport of either electrons or ions. In the first case, disordered materials display lower electrical conductivity than their crystalline counterparts, due to localization of conduction electrons due to disorder, so that electron hopping is the main charge transport mechanism. On the other hand, the same disorder may allow the diffusion of ions through interstitial sites; the ionic conductivity of disordered materials is normally higher than the crystalline counterparts.
This thesis presents an experimental study of the conduction properties and molecular dynamics of molecular solids made of fullerene derivatives (C60Br6, C60(ONa)24) and of dinitrile molecules such as succinonitrile (C2H4(CN)2) and glutaronitrile (C3H6(CN)2). The studied materials display, depending on the case, mainly electronic, protonic, or ionic conduction. The thesis provides insight into the different possible types of charge conduction in organic molecular materials and on related physical processes such as space-charge relaxations.
In C60Br6 we observe n-type electronic conduction below room temperature and a non-trivial phase behavior. The temperature dependence of the dc conductivity of this organic semiconductor is in agreement with the variable-range hopping model. C60(ONa)24 has even richer phase behavior. It is synthesized as a polycrystalline hydrate, and can be obtained as pure material by heating to high temperature. We show that while the pure material is an n-type (electron) semiconductor, exposing it to humid atmosphere leads to a dramatic conductivity enhancement due to charge transport through the hydration layers, which is likely mediated by a proton exchange mechanism as in bulk water and ice. We also show that the dc conductivity of the hydrate is strongly temperature dependent across the dehydration process, and that both pure and hydrated forms display a conductivity-related dynamic process associated with accumulation of electrons at grain boundaries. The presence of water has strong impact on such frequency-dependent charge-accumulation dynamics.
We finally analyze the relaxation dynamics and the ionic conductivity of plastic-crystalline ionic conductors, in particular the plastic cocrystals of succinonitrile with glutaronitrile. In plastic crystals, the molecules occupy lattice sites but undergo free rotational motions about their centers of mass. We find that succinonitrile-glutaronitrile cocrystals are the first ever known plastic crystals to display a perfect correlation between the ion drift and the on-site reorientational dynamics. Doping the cocrystals with Li salts boosts the conductivity but breaks down this perfect correlation. This indicates that the rotation-drift correlation is only valid when charge transport is dominated by self-diffusion of molecular (dinitrile) ions, and that it is a consequence of the correlation between rotational and diffusional time scales.El estudio de los materiales cristalinos juega un papel destacado en la física del estado sólido. Sin embargo, los materiales desordenados son más abundantes en la naturaleza que los cristalinos y, además, muchas de las aplicaciones prácticas utilizan materiales que son débilmente o fuertemente desordenados, como vidrios, líquidos, cristales plásticos, cristales moleculares, polímeros, o cristales líquidos. Desde un punto de vista fundamental, aún carecemos de una comprensión de de los materiales desordenados y de la transición vítrea: la comprensión de las propiedades asociadas desorden requiere el uso de conceptos que se alejan de los aplicables al estado cristalino. Desde una perspectiva aplicada, la investigación en los sólidos desordenados está promovida por la importancia tecnológica de estos materiales en la vida cotidiana. Los sólidos desordenados pueden conducir electricidad por transporte de electrones o de iones. En el primer caso, los materiales desordenados muestran menor conductividad que sus respectivas fases cristalinas, debido a la localización de los electrones de conducción por la existencia de desorden, que da lugar a saltos de electrones como principal mecanismo de transporte de carga. Por otro lado, el mismo desorden puede permitir la difusión de iones a través de intersticios; la conductividad iónica de materiales desordenados es más alta que sus fases homólogas cristalinas. Esta tesis presenta un estudio experimental de la conducción eléctrica y de la dinámica molecular de sólidos moleculares formados por derivados de fullereno (C60Br6, C60(ONa)24) o por moléculas con dos grupos nitrilos (succinonitrila (C2H4(CN)2), glutaronitrila (C3H6 (CN)2)). Estos materiales presentan, según el caso, conducción electrónica, protónica, o iónica. La tesis analiza los diferentes tipos de conducción de carga en materiales moleculares así como los procesos físicos relacionados, tales como las relajaciones de carga espacial. En el material C60Br6 observamos conducción electrónica tipo n y un comportamiento de fase no trivial. La dependencia de la conductividad con la temperatura está de acuerdo con el modelo de salto de rango variable (VRH). El C60(ONa)24 tiene un comportamiento de fase aún más rico. Se sintetiza como un hidrato policristalino, y se puede obtener como material puro por calentamiento. Mientras que el material puro es un semiconductor de tipo n, su exposición a una atmósfera húmeda aumenta la conductividad de forma dramática debido al transporte de carga a través de las capas de hidratación, lo que probablemente se debe a un mecanismo de intercambio de protones como en el agua pura o en el hielo. La conductividad del hidrato depende fuertemente de la temperatura en el proceso de deshidratación. Ambas formas, pura e hidratada, muestran un proceso dinámico asociado a la acumulación de electrones en los límites de grano. La presencia de agua tiene un fuerte impacto en tal proceso. Por último se analizan la dinámica molecular y la conductividad iónica de cristales plásticos, en particular, de las aleaciones moleculares en fase plástica formadas entre la succinonitrila y la glutaronitrila. En las fases plásticas las moléculas ocupan los sitios cristalográficos de la red, pero se encuentran orientacionalmente desordenadas. Se demuestra que las aleaciones succinonitrila-glutaronitrila son los primeros cristales plásticos que se conocen en los que existe una correlación perfecta entre la corriente de iones y la dinámica reorientational de las moléculas en los sitios cristalográficos. El dopaje de las aleaciones con sales de Li aumenta la conductividad pero destruye la correlación anterior, lo que indica que la correlación sólo es válida cuando el transporte de carga está dominado por la difusión de iones moleculares. Tal correlación puede ser consecuencia de una correlación entre las escalas de tiempo de rotación y de difusión.
41
Kramer, Steve Andrew. "Mixed ionic-electronic conduction in rare earth titanate/zirconate pyrochlore compounds." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/26863.
Full text
42
Blom, Christine. "Development of Rare Earth Metal Iron Oxides as Mixed Ionic and Electronic Conductors." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-26125.
Full textAbstract:
In recent years there has been an increasing interest in finding a new and less energy demanding alternative to cryogenic distillation in the production of pure oxygen gas. The use of oxygen permeable membranes has been considered a preferable alternative, and extensive studies into candidate materials for use in these membranes, performed. Problems concerning cationic demixing and breakdown of the material structure has been reported for many of these materials were oxygen is transported through oxygen vacancies usually requiring an operating temperature above 800°C. Lately, an increasing interest in materials that can transport oxygen through oxygen interstitials instead of vacancies has emerged, since oxygen interstitials can be transported at temperatures below 600°C where cationic diffusion is usually prevented. A study of the oxygen storage ability of rare earth ferrites has recently been reported, where an oxygen storage ability of an x=0.5, and a good cycling ability has been found for LuFe2O4. A problem with the use of rare earth ferrites for this purpose is that the powder preparation route involves metallic iron as one of the precursors, requiring the use of a glove box in the preparation of the material. In this study, phase pure powder of another rare earth ferrite, YbFe2O4 has been performed from a conventional solid state synthesis route. Strong indications of the possibility of obtaining the material from a sol-gel synthesis route is also reported. Heat treatment of the material in oxygen atmosphere resulting in an oxygen rich phase, YbFe2O4.5, was quantified from in situ TGA measurements, while an ex. situ heat treatment performed under oxidizing and reducing conditions strongly indicates a good cycling ability of the material. The increase in the oxygen content during heat treatment in oxygen atmosphere took place below 500°C, and is therefore expected to originate from oxygen interstitials being implemented in the structure. A significant change in structure is also observed after heat treatment in oxygen atmosphere, emphasizing this theory. Indications of a p-type conductivity from a van der Pauw measurement is also reported. The new and more convenient powder preparation route, significantly increases the potential of rare earth ferrites for use in oxygen permeable membranes, and a further investigation into their reported multiferroic properties. A replacement of Lu with Yb in the material significantly decreases the material cost, and therefore the use of these materials in up-scale production.
43
Saha, Sujoy. "Exploration of ionic conductors and Li-rich sulfides for all-solid-state batteries." Electronic Thesis or Diss., Sorbonne université, 2020. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2020SORUS041.pdf.
Full textAbstract:
Les besoins croissants en stockage de l’énergie exigent une amélioration continue des batteries lithium-ion. Le mécanisme de redox anionique qui permet d’augmenter la densité d’énergie des électrodes positives mais est associé à divers inconvénients (hystérésis et décroissance de tension, cinétique lente, etc.) qui restent à résoudre. De plus, la sécurité des batteries lithium-ion peut être améliorée en concevant des batteries tout-solide. Dans cette thèse, nous nous sommes d'abord concentrés sur le développement de nouveaux électrolytes solides à base d'oxydes pour des applications dans les batteries tout-solide. Nous avons exploré l’influence du désordre structural sur conductivité ionique des électrolytes solides et montré comment il était possible d’augmenter la conductivité en stabilisant à température ambiante les phases désordonnées présentes à haute température. Ensuite, nous avons conçu des électrodes à base de sulfures riches en Li présentant du rédox anionique, qui en outre présentent une excellente réversibilité. Ainsi, les matériaux d'électrode nouvellement conçus ouvrent une direction possible pour atténuer les problèmes liés au rédox anionique. Enfin, nous avons utilisé les sulfures comme électrode positive dans des batteries tout-solide avec des électrolytes solides à base de sulfures; ces systèmes montrent une excellente cyclabilité, soulignant ainsi l’importance de la compatibilité interfaciale dans les batteries tout-solideGrowing needs for energy storage applications require continuous improvement of the lithium ion batteries (LIB). The anionic redox chemistry has emerged recently as a new paradigm to design high-energy positive electrodes of LIBs, however with some issues (i.e., voltage hysteresis and fading, sluggish kinetics, etc.) that remained to be solved. In addition, the safety of the LIBs can be improved by designing all-solid-state batteries (ASSB). In this thesis, we first focused on the development of new oxide-based solid electrolytes (SE) for applications in ASSBs. We explored the influence of disorder on the ionic conductivity of SEs and demonstrated how to increase the conductivity by stabilizing disordered high-temperature phases. Furthermore, we designed Li-rich layered sulfide electrodes that undergo anionic sulfur redox, with excellent reversibility. Thus, the newly designed electrode materials show a possible direction to mitigate the issues related to anionic redox. Lastly, we used the Li-rich sulfides as positive electrode in ASSB with sulfide-based SEs that demonstrate excellent cyclability, thereby highlighting the importance of interfacial compatibility in ASSBs
44
Cerisier, Jacky. "Caracterisation et etude physico-chimique de conducteurs ioniques afecl::(4) (a : alcalin) et de li::(4)fei::(6) : ionicite des liaisons mecanismes de conduction." Nantes, 1987. http://www.theses.fr/1987NANT2003.
Full text
45
Norman, Colin John. "Synthesis and characterisation of barium strontium cobalt iron oxide mixed ionic and electronic conductors." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/synthesis-and-characterisation-of-barium-strontium-cobalt-iron-oxide-mixed-ionic-and-electronic-conductors(f6a8cb7b-388d-4543-b340-d6d0f33c1d84).html.
Full textAbstract:
Oxygen separation membrane technology is an alternative to cryogenic distillation for the production of oxygen. Barium strontium cobalt iron oxide (BSCF, Ba0.5Sr0.5Co0.8Fe0.2O3-d) is one of the candidate membrane materials for this application. A robust wet-chemical synthetic route for the synthesis of BSCF has been developed. The route comprises reverse precipitation from a mixed metal nitrate solution at pH> 10 and uses a minimum amount of reagents. In particular there are no organic additives which need to be burnt off. All the metal ions precipitated simultaneously but a single phase was not then formed. The phases formed during precipitation, drying and calcining varied with the experimental conditions used. It was shown that ~80% of the barium and strontium precipitated as their mixed carbonate. However, on sintering, a single cubic phase material was formed. The process was capable of variation in the BSCF composition and the addition of copper to the system. The electrical and oxygen permeation properties were measured. The relationship between them was found to be dependent on the lattice parameter, tolerance factor and oxygen non-stoichiometry (d). Values of d greater than 0.5 at high temperature were found to give poor oxygen permeation and an increase in resistance although they did not decompose to the ordered brownmillerite structure. The addition of copper to BSCF by substituting it for iron and cobalt enhanced grain growth during sintering. However, except at the lowest addition level of 0.05 on the B-site, it did not show any oxygen permeation. High temperature x-ray diffraction (HTXRD) and x-ray photoelectron spectroscopy (XPS) studies were carried out. They showed that the thermal expansion coefficient increased at ~400° as loss of oxygen from the material started. As the materials were heated in the XPS surface carbonates were removed and the surface concentration of Ba and Sr ions decreased at 3-500°C although on further heating to 800°C their concentration returned to close to the original values.
46
Armstrong, Tad John. "Oxygen permeation properties of perovskite-related intergrowth oxides exhibiting mixed ionic-electronic conduction /." Digital version accessible at:, 2000. http://wwwlib.umi.com/cr/utexas/main.
Full text
47
Walker, Ethan. "Injection, Transport, and Ionic Interactions of Carriers in Polyacetylene Ionomers as Probed by Near-Infrared Absorbance and Visible Photoresoponse." Thesis, University of Oregon, 2015. http://hdl.handle.net/1794/19331.
Full textAbstract:
While mixed ionic-electronic conductors (MIECs) show promise in a number of different device structures, their successful application has been inhibited by difficulties with characterization. The simultaneous influence of both ionic and electronic systems often foils attempts to quantify material parameters important for rational device design. In many cases, even general models of MIEC function can prove uncertain or controversial.
This dissertation addresses the broader issue of ambiguity in MIEC characterization by exploring near-infrared absorbance as a method of gaining further insight into these systems. In combination with a traditional suite of techniques, this method enables determination of parameters not otherwise accessible. The determination of a concentration-dependant carrier mobility in an MIEC material will be demonstrated, and MIEC conduction in the unipolar regime will be broadly described as a system of electrochemically-supported charge injection. This model will be subsequently expanded to describe an unusual and previously unreported phenomenon of rectification when MIECs are interfaced with otherwise appropriate semiconducting contacts. A model labeled as extracting-electrode space-charge limited current will be described and experimentally demonstrated. Finally, the unique photovoltaic properties of an ionic heterojunction system comprising two MIECs will be examined. The results will be used to gain insight into the role of ionic asymmetry in the behavior of MIEC interfaces.
This dissertation contains coauthored, previously published, and unpublished work.
48
Salvador, Maria Adelaide Cotovio. "Nano-ionics: proton conduction enhancement of electrolytes by heterogeneous doping." Doctoral thesis, Universidade de Aveiro, 2017. http://hdl.handle.net/10773/22456.
Full textAbstract:
Doutoramento em Ciência e Engenharia de MateriaisCondutores protónicos são o cerne funcional de muitos equipamentos de conversão de energia, sensores e controle de luz. Portanto, é muito importante compreender fenómenos interfaciais. O objectivo desta Tese de Doutoramento é o estudo da condutividade protónica de compósitos nano-iónicos obtidos pela dopagem heterogénea de electrólitos fracos com nanopartículas de óxido e materiais mesoporosos, que são essencialmente dieléctricos, através da formação de interfaces condutoras com elevada concentração de protões. Esta investigação baseia-se na dopagem heterogénea de electrólitos fracos tais como imidazol (Iz), benzimidazol (Bz), 1H-1,2,4-triazol (Tz) e pirazol (Pz) com nanopartículas de óxidos metálicos e os correspondentes óxidos mesoporosos, CeO2, TiO2, ZrO2 e BaZrO3. O princípio subjacente é o da criação de zonas de carga espacial com elevada concentração de protões na interface entre o electrólito e o óxido, configurando assim novos tipos de materiais interfaciais do tipo nano-iónico. Numa primeira fase, o trabalho é dedicado à síntese de CeO2, TiO2, ZrO2 e BaZrO3 mesoporosos por nano replicação utilizando SBA-15 ou CMK-3 como moldes. O material molde foi selecionado de forma a minimizar a interacção química entre o molde e os percursores, maximizando assim a pureza da fase de óxido mesoporoso obtido. O óxido de cério foi obtido usando SBA-15, o óxido de zircónio e o óxido de titânio foram preparadas usando ambos os moldes SBA-15 e CMK-3, e o zirconato de bário foi sintetizado unicamente com CMK-3. Numa segunda etapa, medidas de potencial zeta foram usadas para avaliação da carga superficial dos óxidos em contacto com os vários electrólitos, em suspensões aquosas. O potencial zeta diminui com o aumento da fracção do electrólito, o que pode ser explicado assumindo a adsorção selectiva de aniões na superfície dos óxidos. Este efeito é mais evidente com a adição de Iz e Bz do que com a adição de Tz e Pz, em concordância com a menor constante de dissociação apresentada pelos primeiros electrólitos fracos. O enriquecimento dos aniões à superfície tem de ser compensado pelo estabelecimento de regiões de carga ricas em catiões adjacentes à superfície das partículas, o que leva ao desejado efeito mesoscópico do aumento da condutividade. Este efeito foi verificado pelo estudo detalhado de espectroscopia de impedância, o qual mostra que a condutividade protónica, em condições anidras, para os compósitos óxido/electrólito aumenta com o aumento da fracção volúmica das partículas de óxido e com a mesoporosidade. O aumento da condutividade observado pode alcançar cerca de 3 ordens de magnitude em relação a CeO2 e ao electrólito Bz puros. Embora os resultados do aumento da condutividade sejam impressionantes são ainda insuficientes para aplicação tecnológica. Evidências para a contribuição interfacial encontram-se nos espectros de impedância com o aparecimento de semicírculos adicionais, que podem ser correlacionados à área interfacial óxido/electrólito através da fracção volúmica do óxido e da mesoporosidade.
Proton conductors are the functional core of many devices for energy conversion, sensing and light control. Thus, it is very important to understand interfacial phenomena. The main objective of this PhD Thesis is to study the protonic conductivity of nano-ionic composites obtained by heterogeneous doping of weak electrolytes with oxide nanoparticles and mesoporous materials, which are essentially dielectric, via the formation of conducting interfaces with enhanced proton concentration. This investigation is based on the heterogeneous doping of weak proton conducting electrolytes such as imidazole (Iz), benzimidazole (Bz), 1H-1,2,4-triazole (Tz) and pyrazole (Pz) with metal oxide nanoparticles and matching mesoporous counterparts of CeO2, TiO2, ZrO2 and BaZrO3. The underlying principle is the formation of proton-enriched space-charge layers at the electrolyte/particle interface, configuring in this way new types of interfacial materials of nano-ionic type. On a first stage, the work is devoted to the synthesis of mesoporous CeO2, TiO2, ZrO2 and BaZrO3 by nanocasting using suitable SBA-15 silica or CMK-3 carbon hard templates in order to minimize the chemical interaction between the template and the reactant precursors, thus maximizing the phase purity of the obtained mesoporous oxide. Ceria was obtained with SBA-15, zirconia and titania with both SBA-15 and CMK-3, and barium zirconate only with CMK-3. On a second stage, zeta potential measurements were used to assess the oxide surface charge in contact with the various electrolytes, in aqueous suspension. The zeta potential decreases with increasing fraction of electrolyte, which can be explained assuming the selective anion adsorption on the surface of the oxides. This effect is stronger upon addition of Iz and Bz than of Tz and Pz, in agreement with the smaller self-dissociation constants of the former weak electrolytes. The enriched anion surface must be compensated by the establishment of adjacent cation-rich space-charge regions, which produce the desired mesoscopic conductivity enhancement. This effect was verified by detailed impedance spectroscopy studies showing that the proton conductivity in anhydrous conditions of the oxide/electrolyte composites increases with increasing volume fraction of the oxide particle and with the mesoporosity. The observed conductivity enhancement may reach ca. 3 orders of magnitude with respect to pure CeO2 and Bz. While impressive, the attained conductivities are still insufficient for technological application. Evidence for interfacial contribution is found in impedance spectra by additional semicircles, which can be correlated to oxide/electrolyte interfacial area through the oxide volume fraction and mesoporosity.
49
Mokkelbost, Tommy. "Synthesis and Characterization of CeO2- and LaNbO4-based Ionic Conductors." Doctoral thesis, Norwegian University of Science and Technology, Department of Materials Technology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-1762.
Full textAbstract:
Ceramic electrolytes that conduct either oxygen ions or protons at intermediate temperatures are important materials for use in e.g. solid oxide fuel cells, the prime candidate to produce electricity by electrochemical reactions. There are still challenges with respect to the cell performance which have to be solved before solid oxide fuel cells become a commercial success. One of the main topics in this field concerns the enhancement of ionic conductivity at suitable operation temperatures. During the last decade nanocrystalline materials have received considerable attention. Nanocrystalline ionic conductors may have higher ionic conductivity compared to traditional ceramics with grain sizes in the micrometer range.
The aim of this work has been to develop electrolyte ceramic materials with a designed microstructure. CeO2- and LaNbO4-based materials have been prepared through a complete route, from preparation of powders to densification of ceramics including characterization of selected properties. CeO2-based materials are oxygen ion conductors and show higher ionic conductivity compared to the more common yttria stabilized zirconia (YSZ), thus a lower operation temperature is possible. LaNbO4-based materials have recently been suggested as a promising proton conductor stable in CO2/H2O atmosphere.
In Paper I, powder synthesis of nanocrystalline CeO2-based powders (CeO2, Ce0.8Gd0.2O1.9 and Ce0.8Sm0.2O1.9) using combustion synthesis with glycine as fuel and nitrate as oxidizer is reported. The influence of glycine to nitrate (G/N) ratio on the pure CeO2-based powders was investigated. The influence of calcination temperature on crystallite size, surface area and carbonate species remaining from combustion reaction was studied, with special attention to powders prepared using a near-stoichiometric G/N-ratio. A G/N-ratio of 0.55 and calcination at 550°C in oxygen flow resulted in high quality powders with a crystallite size of ~10 nm with low degree of agglomeration due to the vigorous combustion. The G/N-ratio influenced the densification behavior of the powders. A G/N-ratio of 0.55 resulted in excellent sintering properties with an onset of sintering at ~600°C and fully dense materials were obtained at ~1300°C.
In Paper II, three different sintering techniques have been used to prepare dense (>95%) CeO2-based materials from the high-quality powders described in Paper I: Spark plasma sintering, hot pressing and conventional sintering. The three different sintering techniques resulted in different grain sizes, ranging from 160 nm by spark plasma sintering, to 50 μm by conventional sintering mainly due to difference in sintering temperature and the applied pressure. The materials were reduced after hot pressing and a minor reduction was observed after spark plasma sintering. The materials were easily reoxidized at temperatures above 200°C. The electrical conductivity, measured by van der Pauw method, revealed no clear dependence on grain size, but instead a dependence on the sintering method used. The substituted materials prepared by hot pressing had a lower electrical conductivity and higher activation energy compared to the materials prepared by both conventional and spark plasma sintering. Thus, it is proposed that the reduction of Ce observed during hot pressing might be detrimental for the ionic conductivity even after reoxidation. Hardness and fracture toughness, measured by Vickers indentation, were more influenced by chemical composition than the grain size of the materials. Higher fracture toughness and lower hardness were observed for pure CeO2 compared to the substituted materials.
A novel route to prepare large quantity of sub-micron LaNbO4-based powders by spray pyrolysis is presented in Paper III. An aqueous solution containing stable La-EDTA complex and Nb-malic acid complex was spray pyrolysed using an in-house spray pyrolysis unit. The pure, nonagglomerated powders had a particle size of ~0.1 μm, narrow particle size distribution and high purity after calcination at 800°C.
The sintering behavior, microstructure, phase content and electrical conductivity of La1-xAxNbO4 (x = 0, 0.005 and 0.02 and A = Ca, Sr and Ba) prepared by spray pyrolysis is presented in Paper IV. The powders had excellent sintering properties and achieved high density after conventional sintering at 1200°C or as low as 1050°C by hot pressing at 25 MPa. A grain size down to 0.4 μm was achieved by hot pressing. The acceptor doped materials had a more homogenous microstructure due to secondary phases inhibiting grain growth compared to pure LaNbO4. Liquid secondary phase was formed at elevated temperatures in acceptor doped LaNbO4, resulting in tremendous grain growth (~70 μm) and microcracking in La0.98Ba0.02NbO4. The solubility of Sr on La-site in LaNbO4 was determined to 1% at 1500°C, and similar low solubility of CaO and BaO in LaNbO4 was inferred. Protons were found to be the main charge carrier up to 1000°C in wet hydrogen. Higher grain boundary resistivity was observed compared to previous work, possibly due to lower sintering temperature resulting in secondary phases due to lower solubility of AO.
The thermal and mechanical properties of LaNbO4-based materials are presented in Paper V. The materials possessed a ferroelastic to paraelastic phase transition at ~500°C and the linear thermal expansion was significant lower for the paraelastic compared to the ferroelastic phase. The pure LaNbO4 had a significantly lower hardness compared to acceptor doped (Ca, Sr and Ba) LaNbO4 due to large grain size and microcracking. The fracture toughness of La0.98Sr0.02NbO4, measured by SEVNB method, was 1.7±0.2 MPa·m1/2. The ferroelastic properties were confirmed by non-linear stress-strain relationship and remnant strain. The remnant strain decreases with increasing temperature and increasing acceptor doping. The latter was possibly due to secondary phases pinning the ferroelastic domain boundaries.
50
Dervisoglu, Riza. "Local structure analysis of solid state ionic conductors, perovskite-derived structures by NMR and computational studies." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.590243.
Full textAbstract:
In this work, local environments of ions in solid oxide fuel cell (SOFC) electrolyte materials with perovskite and perovskite-derived crystallographic structures, i.e. Ba₂In₂O₅, Ba₂(In₁₋ₓGaₓ)₂O₅ and Ba₂In₂O₄(OH)₂, were investigated for their high ionic (O²⁻ and H⁺) mobility at elevated temperatures. Two general methods were employed in this investigation; first, computational methods, such as density functional theory (DFT), gauge including projector augmented wave (GIPAW), cluster expansion (CE) and Monte Carlo simulations (MC); second, experimental methods, such as nuclear magnetic resonance (NMR), X-ray scattering (both powder diffraction and pair distribution function (PDF) analysis) and thermo-gravimetric analysis (TGA). The parent material, Ba₂In₂O₅, has inherent oxygen vacancies which allow for fast O₂₋ ion mobility at elevated temperatures and for hydration of the material needless of doping. We improve a previous NMR study of Ba₂In₂O₅ by Adler et al. [1], assigning all three oxygen crystallographic sites to their relevant NMR peaks and investigate the high temperature structure. We then study the iso-valent doping of Ga into the In site resulting in Ba₂(In₁₋ₓGaₓ)₂O₅. While Yao et al. [2] find that Ga doping levels higher than 20% form a stable cubic structure, our findings indicate that Ga doping results in a phase segregation. However our findings for quenched samples are no different than those of Yao et al. [2]. Lastly we study the hydrated form of the parent material, Ba₂In₂O₄(OH)₂, which has high H⁺ ion mobility above 180°C. We observe at least three possible hydrogen sites with local environments slightly different from the previous neutron diffraction study by Jayaraman et al. [3]. In contrast to the observation by Jayaraman et al. [3] of the hydrogen presence in all O2 layers we find an alternating occupancy of hydrogens in those layers.